diff --git a/Libraries/LibJS/Runtime/Temporal/AbstractOperations.cpp b/Libraries/LibJS/Runtime/Temporal/AbstractOperations.cpp
index addbd5cb440..fe7850367fb 100644
--- a/Libraries/LibJS/Runtime/Temporal/AbstractOperations.cpp
+++ b/Libraries/LibJS/Runtime/Temporal/AbstractOperations.cpp
@@ -475,12 +475,16 @@ ThrowCompletionOr<RelativeTo> get_temporal_relative_to_option(VM& vm, Object con
     if (value.is_undefined())
         return RelativeTo { .plain_relative_to = {}, .zoned_relative_to = {} };
 
-    // FIXME: 3. Let offsetBehaviour be OPTION.
-    // FIXME: 4. Let matchBehaviour be MATCH-EXACTLY.
+    // 3. Let offsetBehaviour be OPTION.
+    auto offset_behavior = OffsetBehavior::Option;
+
+    // 4. Let matchBehaviour be MATCH-EXACTLY.
+    auto match_behavior = MatchBehavior::MatchExactly;
 
     String calendar;
     Optional<String> time_zone;
     Optional<String> offset_string;
+
     ISODate iso_date;
     Variant<ParsedISODateTime::StartOfDay, Time> time { Time {} };
 
@@ -488,8 +492,11 @@ ThrowCompletionOr<RelativeTo> get_temporal_relative_to_option(VM& vm, Object con
     if (value.is_object()) {
         auto& object = value.as_object();
 
-        // FIXME: a. If value has an [[InitializedTemporalZonedDateTime]] internal slot, then
-        // FIXME:     i. Return the Record { [[PlainRelativeTo]]: undefined, [[ZonedRelativeTo]]: value }.
+        // a. If value has an [[InitializedTemporalZonedDateTime]] internal slot, then
+        if (is<ZonedDateTime>(object)) {
+            // i. Return the Record { [[PlainRelativeTo]]: undefined, [[ZonedRelativeTo]]: value }.
+            return RelativeTo { .plain_relative_to = {}, .zoned_relative_to = static_cast<ZonedDateTime&>(object) };
+        }
 
         // b. If value has an [[InitializedTemporalDate]] internal slot, then
         if (is<PlainDate>(object)) {
@@ -527,7 +534,8 @@ ThrowCompletionOr<RelativeTo> get_temporal_relative_to_option(VM& vm, Object con
 
         // i. If offsetString is UNSET, then
         if (!offset_string.has_value()) {
-            // FIXME: i. Set offsetBehaviour to WALL.
+            // i. Set offsetBehaviour to WALL.
+            offset_behavior = OffsetBehavior::Wall;
         }
 
         // j. Let isoDate be result.[[ISODate]].
@@ -563,14 +571,17 @@ ThrowCompletionOr<RelativeTo> get_temporal_relative_to_option(VM& vm, Object con
 
             // ii. If result.[[TimeZone]].[[Z]] is true, then
             if (result.time_zone.z_designator) {
-                // FIXME: 1. Set offsetBehaviour to EXACT.
+                // 1. Set offsetBehaviour to EXACT.
+                offset_behavior = OffsetBehavior::Exact;
             }
             // iii. Else if offsetString is EMPTY, then
             else if (!offset_string.has_value()) {
-                // FIXME: 1. Set offsetBehaviour to WALL.
+                // 1. Set offsetBehaviour to WALL.
+                offset_behavior = OffsetBehavior::Wall;
             }
 
-            // FIXME: iv. Set matchBehaviour to MATCH-MINUTES.
+            // iv. Set matchBehaviour to MATCH-MINUTES.
+            match_behavior = MatchBehavior::MatchMinutes;
         }
 
         // g. Let calendar be result.[[Calendar]].
@@ -596,15 +607,27 @@ ThrowCompletionOr<RelativeTo> get_temporal_relative_to_option(VM& vm, Object con
         return RelativeTo { .plain_relative_to = plain_date, .zoned_relative_to = {} };
     }
 
-    // FIXME: 8. If offsetBehaviour is OPTION, then
-    // FIXME:     a. Let offsetNs be ! ParseDateTimeUTCOffset(offsetString).
-    // FIXME: 9. Else,
-    // FIXME:     a. Let offsetNs be 0.
-    // FIXME: 10. Let epochNanoseconds be ? InterpretISODateTimeOffset(isoDate, time, offsetBehaviour, offsetNs, timeZone, compatible, reject, matchBehaviour).
-    // FIXME: 11. Let zonedRelativeTo be ! CreateTemporalZonedDateTime(epochNanoseconds, timeZone, calendar).
-    // FIXME: 12. Return the Record { [[PlainRelativeTo]]: undefined, [[ZonedRelativeTo]]: zonedRelativeTo }.
+    double offset_nanoseconds = 0;
 
-    return RelativeTo { .plain_relative_to = {}, .zoned_relative_to = {} };
+    // 8. If offsetBehaviour is OPTION, then
+    if (offset_behavior == OffsetBehavior::Option) {
+        // a. Let offsetNs be ! ParseDateTimeUTCOffset(offsetString).
+        offset_nanoseconds = parse_date_time_utc_offset(*offset_string);
+    }
+    // 9. Else,
+    else {
+        // a. Let offsetNs be 0.
+        offset_nanoseconds = 0;
+    }
+
+    // 10. Let epochNanoseconds be ? InterpretISODateTimeOffset(isoDate, time, offsetBehaviour, offsetNs, timeZone, COMPATIBLE, REJECT, matchBehaviour).
+    auto epoch_nanoseconds = TRY(interpret_iso_date_time_offset(vm, iso_date, time, offset_behavior, offset_nanoseconds, *time_zone, Disambiguation::Compatible, OffsetOption::Reject, match_behavior));
+
+    // 11. Let zonedRelativeTo be ! CreateTemporalZonedDateTime(epochNanoseconds, timeZone, calendar).
+    auto zoned_relative_to = MUST(create_temporal_zoned_date_time(vm, BigInt::create(vm, move(epoch_nanoseconds)), time_zone.release_value(), move(calendar)));
+
+    // 12. Return the Record { [[PlainRelativeTo]]: undefined, [[ZonedRelativeTo]]: zonedRelativeTo }.
+    return RelativeTo { .plain_relative_to = {}, .zoned_relative_to = zoned_relative_to };
 }
 
 // 13.19 LargerOfTwoTemporalUnits ( u1, u2 ), https://tc39.es/proposal-temporal/#sec-temporal-largeroftwotemporalunits
diff --git a/Libraries/LibJS/Runtime/Temporal/AbstractOperations.h b/Libraries/LibJS/Runtime/Temporal/AbstractOperations.h
index 89afe895af4..5f9083f9656 100644
--- a/Libraries/LibJS/Runtime/Temporal/AbstractOperations.h
+++ b/Libraries/LibJS/Runtime/Temporal/AbstractOperations.h
@@ -143,8 +143,8 @@ struct SecondsStringPrecision {
 };
 
 struct RelativeTo {
-    GC::Ptr<PlainDate> plain_relative_to; // [[PlainRelativeTo]]
-    GC::Ptr<Object> zoned_relative_to;    // FIXME: [[ZonedRelativeTo]]
+    GC::Ptr<PlainDate> plain_relative_to;     // [[PlainRelativeTo]]
+    GC::Ptr<ZonedDateTime> zoned_relative_to; // [[ZonedRelativeTo]]
 };
 
 struct DifferenceSettings {
diff --git a/Libraries/LibJS/Runtime/Temporal/DurationConstructor.cpp b/Libraries/LibJS/Runtime/Temporal/DurationConstructor.cpp
index b36c25c42f9..17b071d04ce 100644
--- a/Libraries/LibJS/Runtime/Temporal/DurationConstructor.cpp
+++ b/Libraries/LibJS/Runtime/Temporal/DurationConstructor.cpp
@@ -9,6 +9,7 @@
 #include <LibJS/Runtime/Temporal/AbstractOperations.h>
 #include <LibJS/Runtime/Temporal/Duration.h>
 #include <LibJS/Runtime/Temporal/DurationConstructor.h>
+#include <LibJS/Runtime/Temporal/ZonedDateTime.h>
 
 namespace JS::Temporal {
 
@@ -149,12 +150,25 @@ JS_DEFINE_NATIVE_FUNCTION(DurationConstructor::compare)
 
     // 12. If zonedRelativeTo is not undefined, and either TemporalUnitCategory(largestUnit1) or TemporalUnitCategory(largestUnit2) is date, then
     if (zoned_relative_to && (temporal_unit_category(largest_unit1) == UnitCategory::Date || temporal_unit_category(largest_unit2) == UnitCategory::Date)) {
-        // FIXME: a. Let timeZone be zonedRelativeTo.[[TimeZone]].
-        // FIXME: b. Let calendar be zonedRelativeTo.[[Calendar]].
-        // FIXME: c. Let after1 be ? AddZonedDateTime(zonedRelativeTo.[[EpochNanoseconds]], timeZone, calendar, duration1, constrain).
-        // FIXME: d. Let after2 be ? AddZonedDateTime(zonedRelativeTo.[[EpochNanoseconds]], timeZone, calendar, duration2, constrain).
-        // FIXME: e. If after1 > after2, return 1𝔽.
-        // FIXME: f. If after1 < after2, return -1𝔽.
+        // a. Let timeZone be zonedRelativeTo.[[TimeZone]].
+        auto const time_zone = zoned_relative_to->time_zone();
+
+        // b. Let calendar be zonedRelativeTo.[[Calendar]].
+        auto const& calendar = zoned_relative_to->calendar();
+
+        // c. Let after1 be ? AddZonedDateTime(zonedRelativeTo.[[EpochNanoseconds]], timeZone, calendar, duration1, CONSTRAIN).
+        auto after1 = TRY(add_zoned_date_time(vm, zoned_relative_to->epoch_nanoseconds()->big_integer(), time_zone, calendar, duration1, Overflow::Constrain));
+
+        // d. Let after2 be ? AddZonedDateTime(zonedRelativeTo.[[EpochNanoseconds]], timeZone, calendar, duration2, CONSTRAIN).
+        auto after2 = TRY(add_zoned_date_time(vm, zoned_relative_to->epoch_nanoseconds()->big_integer(), time_zone, calendar, duration2, Overflow::Constrain));
+
+        // e. If after1 > after2, return 1𝔽.
+        if (after1 > after2)
+            return 1;
+
+        // f. If after1 < after2, return -1𝔽.
+        if (after1 < after2)
+            return -1;
 
         // g. Return +0𝔽.
         return 0;
diff --git a/Libraries/LibJS/Runtime/Temporal/DurationPrototype.cpp b/Libraries/LibJS/Runtime/Temporal/DurationPrototype.cpp
index 5035de8ca05..59432040299 100644
--- a/Libraries/LibJS/Runtime/Temporal/DurationPrototype.cpp
+++ b/Libraries/LibJS/Runtime/Temporal/DurationPrototype.cpp
@@ -11,6 +11,7 @@
 #include <LibJS/Runtime/Temporal/PlainDate.h>
 #include <LibJS/Runtime/Temporal/PlainDateTime.h>
 #include <LibJS/Runtime/Temporal/PlainTime.h>
+#include <LibJS/Runtime/Temporal/ZonedDateTime.h>
 
 namespace JS::Temporal {
 
@@ -347,11 +348,20 @@ JS_DEFINE_NATIVE_FUNCTION(DurationPrototype::round)
         // a. Let internalDuration be ToInternalDurationRecord(duration).
         auto internal_duration = to_internal_duration_record(vm, duration);
 
-        // FIXME: b. Let timeZone be zonedRelativeTo.[[TimeZone]].
-        // FIXME: c. Let calendar be zonedRelativeTo.[[Calendar]].
-        // FIXME: d. Let relativeEpochNs be zonedRelativeTo.[[EpochNanoseconds]].
-        // FIXME: e. Let targetEpochNs be ? AddZonedDateTime(relativeEpochNs, timeZone, calendar, internalDuration, constrain).
-        // FIXME: f. Set internalDuration to ? DifferenceZonedDateTimeWithRounding(relativeEpochNs, targetEpochNs, timeZone, calendar, largestUnit, roundingIncrement, smallestUnit, roundingMode).
+        // b. Let timeZone be zonedRelativeTo.[[TimeZone]].
+        auto const& time_zone = zoned_relative_to->time_zone();
+
+        // c. Let calendar be zonedRelativeTo.[[Calendar]].
+        auto const& calendar = zoned_relative_to->calendar();
+
+        // d. Let relativeEpochNs be zonedRelativeTo.[[EpochNanoseconds]].
+        auto const& relative_epoch_nanoseconds = zoned_relative_to->epoch_nanoseconds()->big_integer();
+
+        // e. Let targetEpochNs be ? AddZonedDateTime(relativeEpochNs, timeZone, calendar, internalDuration, CONSTRAIN).
+        auto target_epoch_nanoseconds = TRY(add_zoned_date_time(vm, relative_epoch_nanoseconds, time_zone, calendar, internal_duration, Overflow::Constrain));
+
+        // f. Set internalDuration to ? DifferenceZonedDateTimeWithRounding(relativeEpochNs, targetEpochNs, timeZone, calendar, largestUnit, roundingIncrement, smallestUnit, roundingMode).
+        internal_duration = TRY(difference_zoned_date_time_with_rounding(vm, relative_epoch_nanoseconds, target_epoch_nanoseconds, time_zone, calendar, largest_unit_value, rounding_increment, smallest_unit_value, rounding_mode));
 
         // g. If TemporalUnitCategory(largestUnit) is date, set largestUnit to hour.
         if (temporal_unit_category(largest_unit_value) == UnitCategory::Date)
@@ -479,12 +489,23 @@ JS_DEFINE_NATIVE_FUNCTION(DurationPrototype::total)
 
     // 11. If zonedRelativeTo is not undefined, then
     if (zoned_relative_to) {
-        // FIXME: a. Let internalDuration be ToInternalDurationRecord(duration).
-        // FIXME: b. Let timeZone be zonedRelativeTo.[[TimeZone]].
-        // FIXME: c. Let calendar be zonedRelativeTo.[[Calendar]].
-        // FIXME: d. Let relativeEpochNs be zonedRelativeTo.[[EpochNanoseconds]].
-        // FIXME: e. Let targetEpochNs be ? AddZonedDateTime(relativeEpochNs, timeZone, calendar, internalDuration, constrain).
-        // FIXME: f. Let total be ? DifferenceZonedDateTimeWithTotal(relativeEpochNs, targetEpochNs, timeZone, calendar, unit).
+        // a. Let internalDuration be ToInternalDurationRecord(duration).
+        auto internal_duration = to_internal_duration_record(vm, duration);
+
+        // b. Let timeZone be zonedRelativeTo.[[TimeZone]].
+        auto const time_zone = zoned_relative_to->time_zone();
+
+        // c. Let calendar be zonedRelativeTo.[[Calendar]].
+        auto const& calendar = zoned_relative_to->calendar();
+
+        // d. Let relativeEpochNs be zonedRelativeTo.[[EpochNanoseconds]].
+        auto const& relative_epoch_nanoseconds = zoned_relative_to->epoch_nanoseconds()->big_integer();
+
+        // e. Let targetEpochNs be ? AddZonedDateTime(relativeEpochNs, timeZone, calendar, internalDuration, CONSTRAIN).
+        auto target_epoch_nanoseconds = TRY(add_zoned_date_time(vm, relative_epoch_nanoseconds, time_zone, calendar, internal_duration, Overflow::Constrain));
+
+        // f. Let total be ? DifferenceZonedDateTimeWithTotal(relativeEpochNs, targetEpochNs, timeZone, calendar, unit).
+        total = TRY(difference_zoned_date_time_with_total(vm, relative_epoch_nanoseconds, target_epoch_nanoseconds, time_zone, calendar, unit));
     }
     // 12. Else if plainRelativeTo is not undefined, then
     else if (plain_relative_to) {
diff --git a/Libraries/LibJS/Runtime/Temporal/ZonedDateTime.cpp b/Libraries/LibJS/Runtime/Temporal/ZonedDateTime.cpp
index 7fab84a3f79..5dd7bde51ca 100644
--- a/Libraries/LibJS/Runtime/Temporal/ZonedDateTime.cpp
+++ b/Libraries/LibJS/Runtime/Temporal/ZonedDateTime.cpp
@@ -9,9 +9,11 @@
 #include <LibJS/Runtime/AbstractOperations.h>
 #include <LibJS/Runtime/Date.h>
 #include <LibJS/Runtime/Temporal/Calendar.h>
+#include <LibJS/Runtime/Temporal/Duration.h>
 #include <LibJS/Runtime/Temporal/Instant.h>
 #include <LibJS/Runtime/Temporal/PlainDate.h>
 #include <LibJS/Runtime/Temporal/PlainDateTime.h>
+#include <LibJS/Runtime/Temporal/PlainTime.h>
 #include <LibJS/Runtime/Temporal/TimeZone.h>
 #include <LibJS/Runtime/Temporal/ZonedDateTime.h>
 #include <LibJS/Runtime/Temporal/ZonedDateTimeConstructor.h>
@@ -317,4 +319,152 @@ ThrowCompletionOr<GC::Ref<ZonedDateTime>> create_temporal_zoned_date_time(VM& vm
     return object;
 }
 
+// 6.5.5 AddZonedDateTime ( epochNanoseconds, timeZone, calendar, duration, overflow ), https://tc39.es/proposal-temporal/#sec-temporal-addzoneddatetime
+ThrowCompletionOr<Crypto::SignedBigInteger> add_zoned_date_time(VM& vm, Crypto::SignedBigInteger const& epoch_nanoseconds, StringView time_zone, StringView calendar, InternalDuration const& duration, Overflow overflow)
+{
+    // 1. If DateDurationSign(duration.[[Date]]) = 0, then
+    if (date_duration_sign(duration.date) == 0) {
+        // a. Return ? AddInstant(epochNanoseconds, duration.[[Time]]).
+        return TRY(add_instant(vm, epoch_nanoseconds, duration.time));
+    }
+
+    // 2. Let isoDateTime be GetISODateTimeFor(timeZone, epochNanoseconds).
+    auto iso_date_time = get_iso_date_time_for(time_zone, epoch_nanoseconds);
+
+    // 3. Let addedDate be ? CalendarDateAdd(calendar, isoDateTime.[[ISODate]], duration.[[Date]], overflow).
+    auto added_date = TRY(calendar_date_add(vm, calendar, iso_date_time.iso_date, duration.date, overflow));
+
+    // 4. Let intermediateDateTime be CombineISODateAndTimeRecord(addedDate, isoDateTime.[[Time]]).
+    auto intermediate_date_time = combine_iso_date_and_time_record(added_date, iso_date_time.time);
+
+    // 5. If ISODateTimeWithinLimits(intermediateDateTime) is false, throw a RangeError exception.
+    if (!iso_date_time_within_limits(intermediate_date_time))
+        return vm.throw_completion<RangeError>(ErrorType::TemporalInvalidISODateTime);
+
+    // 6. Let intermediateNs be ! GetEpochNanosecondsFor(timeZone, intermediateDateTime, COMPATIBLE).
+    auto intermediate_nanoseconds = MUST(get_epoch_nanoseconds_for(vm, time_zone, intermediate_date_time, Disambiguation::Compatible));
+
+    // 7. Return ? AddInstant(intermediateNs, duration.[[Time]]).
+    return TRY(add_instant(vm, intermediate_nanoseconds, duration.time));
+}
+
+// 6.5.6 DifferenceZonedDateTime ( ns1, ns2, timeZone, calendar, largestUnit ), https://tc39.es/proposal-temporal/#sec-temporal-differencezoneddatetime
+ThrowCompletionOr<InternalDuration> difference_zoned_date_time(VM& vm, Crypto::SignedBigInteger const& nanoseconds1, Crypto::SignedBigInteger const& nanoseconds2, StringView time_zone, StringView calendar, Unit largest_unit)
+{
+    // 1. If ns1 = ns2, return ! CombineDateAndTimeDuration(ZeroDateDuration(), 0).
+    if (nanoseconds1 == nanoseconds2)
+        return MUST(combine_date_and_time_duration(vm, zero_date_duration(vm), TimeDuration { 0 }));
+
+    // 2. Let startDateTime be GetISODateTimeFor(timeZone, ns1).
+    auto start_date_time = get_iso_date_time_for(time_zone, nanoseconds1);
+
+    // 3. Let endDateTime be GetISODateTimeFor(timeZone, ns2).
+    auto end_date_time = get_iso_date_time_for(time_zone, nanoseconds2);
+
+    // 4. If ns2 - ns1 < 0, let sign be -1; else let sign be 1.
+    double sign = nanoseconds2 < nanoseconds1 ? -1 : 1;
+
+    // 5. If sign = 1, let maxDayCorrection be 2; else let maxDayCorrection be 1.
+    double max_day_correction = sign == 1 ? 2 : 1;
+
+    // 6. Let dayCorrection be 0.
+    double day_correction = 0;
+
+    // 7. Let timeDuration be DifferenceTime(startDateTime.[[Time]], endDateTime.[[Time]]).
+    auto time_duration = difference_time(start_date_time.time, end_date_time.time);
+
+    // 8. If TimeDurationSign(timeDuration) = -sign, set dayCorrection to dayCorrection + 1.
+    if (time_duration_sign(time_duration) == -sign)
+        ++day_correction;
+
+    // 9. Let success be false.
+    auto success = false;
+
+    ISODateTime intermediate_date_time;
+
+    // 10. Repeat, while dayCorrection ≤ maxDayCorrection and success is false,
+    while (day_correction <= max_day_correction && !success) {
+        // a. Let intermediateDate be BalanceISODate(endDateTime.[[ISODate]].[[Year]], endDateTime.[[ISODate]].[[Month]], endDateTime.[[ISODate]].[[Day]] - dayCorrection × sign).
+        auto intermediate_date = balance_iso_date(end_date_time.iso_date.year, end_date_time.iso_date.month, static_cast<double>(end_date_time.iso_date.day) - (day_correction * sign));
+
+        // b. Let intermediateDateTime be CombineISODateAndTimeRecord(intermediateDate, startDateTime.[[Time]]).
+        intermediate_date_time = combine_iso_date_and_time_record(intermediate_date, start_date_time.time);
+
+        // c. Let intermediateNs be ? GetEpochNanosecondsFor(timeZone, intermediateDateTime, COMPATIBLE).
+        auto intermediate_nanoseconds = TRY(get_epoch_nanoseconds_for(vm, time_zone, intermediate_date_time, Disambiguation::Compatible));
+
+        // d. Set timeDuration to TimeDurationFromEpochNanosecondsDifference(ns2, intermediateNs).
+        time_duration = time_duration_from_epoch_nanoseconds_difference(nanoseconds2, intermediate_nanoseconds);
+
+        // e. Let timeSign be TimeDurationSign(timeDuration).
+        auto time_sign = time_duration_sign(time_duration);
+
+        // f. If sign ≠ -timeSign, then
+        if (sign != -time_sign) {
+            // i. Set success to true.
+            success = true;
+        }
+
+        // g. Set dayCorrection to dayCorrection + 1.
+        ++day_correction;
+    }
+
+    // 11. Assert: success is true.
+    VERIFY(success);
+
+    // 12. Let dateLargestUnit be LargerOfTwoTemporalUnits(largestUnit, DAY).
+    auto date_largest_unit = larger_of_two_temporal_units(largest_unit, Unit::Day);
+
+    // 13. Let dateDifference be CalendarDateUntil(calendar, startDateTime.[[ISODate]], intermediateDateTime.[[ISODate]], dateLargestUnit).
+    auto date_difference = calendar_date_until(vm, calendar, start_date_time.iso_date, intermediate_date_time.iso_date, date_largest_unit);
+
+    // 14. Return ? CombineDateAndTimeDuration(dateDifference, timeDuration).
+    return TRY(combine_date_and_time_duration(vm, date_difference, move(time_duration)));
+}
+
+// 6.5.7 DifferenceZonedDateTimeWithRounding ( ns1, ns2, timeZone, calendar, largestUnit, roundingIncrement, smallestUnit, roundingMode ), https://tc39.es/proposal-temporal/#sec-temporal-differencezoneddatetimewithrounding
+ThrowCompletionOr<InternalDuration> difference_zoned_date_time_with_rounding(VM& vm, Crypto::SignedBigInteger const& nanoseconds1, Crypto::SignedBigInteger const& nanoseconds2, StringView time_zone, StringView calendar, Unit largest_unit, u64 rounding_increment, Unit smallest_unit, RoundingMode rounding_mode)
+{
+    // 1. If TemporalUnitCategory(largestUnit) is TIME, then
+    if (temporal_unit_category(largest_unit) == UnitCategory::Time) {
+        // a. Return DifferenceInstant(ns1, ns2, roundingIncrement, smallestUnit, roundingMode).
+        return difference_instant(vm, nanoseconds1, nanoseconds2, rounding_increment, smallest_unit, rounding_mode);
+    }
+
+    // 2. Let difference be ? DifferenceZonedDateTime(ns1, ns2, timeZone, calendar, largestUnit).
+    auto difference = TRY(difference_zoned_date_time(vm, nanoseconds1, nanoseconds2, time_zone, calendar, largest_unit));
+
+    // 3. If smallestUnit is NANOSECOND and roundingIncrement = 1, return difference.
+    if (smallest_unit == Unit::Nanosecond && rounding_increment == 1)
+        return difference;
+
+    // 4. Let dateTime be GetISODateTimeFor(timeZone, ns1).
+    auto date_time = get_iso_date_time_for(time_zone, nanoseconds1);
+
+    // 5. Return ? RoundRelativeDuration(difference, ns2, dateTime, timeZone, calendar, largestUnit, roundingIncrement, smallestUnit, roundingMode).
+    return TRY(round_relative_duration(vm, difference, nanoseconds2, date_time, time_zone, calendar, largest_unit, rounding_increment, smallest_unit, rounding_mode));
+}
+
+// 6.5.8 DifferenceZonedDateTimeWithTotal ( ns1, ns2, timeZone, calendar, unit ), https://tc39.es/proposal-temporal/#sec-temporal-differencezoneddatetimewithtotal
+ThrowCompletionOr<Crypto::BigFraction> difference_zoned_date_time_with_total(VM& vm, Crypto::SignedBigInteger const& nanoseconds1, Crypto::SignedBigInteger const& nanoseconds2, StringView time_zone, StringView calendar, Unit unit)
+{
+    // 1. If TemporalUnitCategory(unit) is TIME, then
+    if (temporal_unit_category(unit) == UnitCategory::Time) {
+        // a. Let difference be TimeDurationFromEpochNanosecondsDifference(ns2, ns1).
+        auto difference = time_duration_from_epoch_nanoseconds_difference(nanoseconds2, nanoseconds1);
+
+        // b. Return TotalTimeDuration(difference, unit).
+        return total_time_duration(difference, unit);
+    }
+
+    // 2. Let difference be ? DifferenceZonedDateTime(ns1, ns2, timeZone, calendar, unit).
+    auto difference = TRY(difference_zoned_date_time(vm, nanoseconds1, nanoseconds2, time_zone, calendar, unit));
+
+    // 3. Let dateTime be GetISODateTimeFor(timeZone, ns1).
+    auto date_time = get_iso_date_time_for(time_zone, nanoseconds1);
+
+    // 4. Return ? TotalRelativeDuration(difference, ns2, dateTime, timeZone, calendar, unit).
+    return TRY(total_relative_duration(vm, difference, nanoseconds2, date_time, time_zone, calendar, unit));
+}
+
 }
diff --git a/Libraries/LibJS/Runtime/Temporal/ZonedDateTime.h b/Libraries/LibJS/Runtime/Temporal/ZonedDateTime.h
index bc63c65081d..bd50ea1234f 100644
--- a/Libraries/LibJS/Runtime/Temporal/ZonedDateTime.h
+++ b/Libraries/LibJS/Runtime/Temporal/ZonedDateTime.h
@@ -7,6 +7,7 @@
 
 #pragma once
 
+#include <LibCrypto/BigFraction/BigFraction.h>
 #include <LibJS/Runtime/BigInt.h>
 #include <LibJS/Runtime/Completion.h>
 #include <LibJS/Runtime/Object.h>
@@ -50,5 +51,9 @@ enum class MatchBehavior {
 ThrowCompletionOr<Crypto::SignedBigInteger> interpret_iso_date_time_offset(VM&, ISODate, Variant<ParsedISODateTime::StartOfDay, Time> const&, OffsetBehavior, double offset_nanoseconds, StringView time_zone, Disambiguation, OffsetOption, MatchBehavior);
 ThrowCompletionOr<GC::Ref<ZonedDateTime>> to_temporal_zoned_date_time(VM&, Value item, Value options = js_undefined());
 ThrowCompletionOr<GC::Ref<ZonedDateTime>> create_temporal_zoned_date_time(VM&, BigInt const& epoch_nanoseconds, String time_zone, String calendar, GC::Ptr<FunctionObject> new_target = {});
+ThrowCompletionOr<Crypto::SignedBigInteger> add_zoned_date_time(VM&, Crypto::SignedBigInteger const& epoch_nanoseconds, StringView time_zone, StringView calendar, InternalDuration const&, Overflow);
+ThrowCompletionOr<InternalDuration> difference_zoned_date_time(VM&, Crypto::SignedBigInteger const& nanoseconds1, Crypto::SignedBigInteger const& nanoseconds2, StringView time_zone, StringView calendar, Unit largest_unit);
+ThrowCompletionOr<InternalDuration> difference_zoned_date_time_with_rounding(VM&, Crypto::SignedBigInteger const& nanoseconds1, Crypto::SignedBigInteger const& nanoseconds2, StringView time_zone, StringView calendar, Unit largest_unit, u64 rounding_increment, Unit smallest_unit, RoundingMode);
+ThrowCompletionOr<Crypto::BigFraction> difference_zoned_date_time_with_total(VM&, Crypto::SignedBigInteger const& nanoseconds1, Crypto::SignedBigInteger const& nanoseconds2, StringView time_zone, StringView calendar, Unit);
 
 }
diff --git a/Libraries/LibJS/Tests/builtins/Temporal/Duration/Duration.compare.js b/Libraries/LibJS/Tests/builtins/Temporal/Duration/Duration.compare.js
index 3eefcd66808..ab0568d5f9a 100644
--- a/Libraries/LibJS/Tests/builtins/Temporal/Duration/Duration.compare.js
+++ b/Libraries/LibJS/Tests/builtins/Temporal/Duration/Duration.compare.js
@@ -47,6 +47,26 @@ describe("correct behavior", () => {
         });
         expect(result).toBe(-1);
     });
+
+    test("relative to zoned date time", () => {
+        const oneMonth = new Temporal.Duration(0, 1);
+        const thirtyDays = new Temporal.Duration(0, 0, 0, 30);
+
+        let result = Temporal.Duration.compare(oneMonth, thirtyDays, {
+            relativeTo: Temporal.ZonedDateTime.from("2018-04-01[UTC]"),
+        });
+        expect(result).toBe(0);
+
+        result = Temporal.Duration.compare(oneMonth, thirtyDays, {
+            relativeTo: Temporal.ZonedDateTime.from("2018-03-01[UTC]"),
+        });
+        expect(result).toBe(1);
+
+        result = Temporal.Duration.compare(oneMonth, thirtyDays, {
+            relativeTo: Temporal.ZonedDateTime.from("2018-02-01[UTC]"),
+        });
+        expect(result).toBe(-1);
+    });
 });
 
 describe("errors", () => {
diff --git a/Libraries/LibJS/Tests/builtins/Temporal/Duration/Duration.prototype.round.js b/Libraries/LibJS/Tests/builtins/Temporal/Duration/Duration.prototype.round.js
index 731cd68d072..b7523bafcf0 100644
--- a/Libraries/LibJS/Tests/builtins/Temporal/Duration/Duration.prototype.round.js
+++ b/Libraries/LibJS/Tests/builtins/Temporal/Duration/Duration.prototype.round.js
@@ -98,6 +98,20 @@ describe("correct behavior", () => {
             expect(result.months).toBe(1);
         });
     });
+
+    test("relative to zoned date time", () => {
+        const duration = new Temporal.Duration(0, 0, 0, 31);
+
+        [
+            "2000-01-01[UTC]",
+            "2000-01-01T00:00[UTC]",
+            "2000-01-01T00:00+00:00[UTC]",
+            "2000-01-01T00:00+00:00[UTC][u-ca=iso8601]",
+        ].forEach(relativeTo => {
+            const result = duration.round({ largestUnit: "months", relativeTo });
+            expect(result.months).toBe(1);
+        });
+    });
 });
 
 describe("errors", () => {
diff --git a/Libraries/LibJS/Tests/builtins/Temporal/Duration/Duration.prototype.total.js b/Libraries/LibJS/Tests/builtins/Temporal/Duration/Duration.prototype.total.js
index 1c31188e142..42a4e7cebb5 100644
--- a/Libraries/LibJS/Tests/builtins/Temporal/Duration/Duration.prototype.total.js
+++ b/Libraries/LibJS/Tests/builtins/Temporal/Duration/Duration.prototype.total.js
@@ -25,6 +25,20 @@ describe("correct behavior", () => {
             expect(result).toBe(1);
         });
     });
+
+    test("relative to zoned date time", () => {
+        const duration = new Temporal.Duration(0, 0, 0, 31);
+
+        [
+            "2000-01-01[UTC]",
+            "2000-01-01T00:00[UTC]",
+            "2000-01-01T00:00+00:00[UTC]",
+            "2000-01-01T00:00+00:00[UTC][u-ca=iso8601]",
+        ].forEach(relativeTo => {
+            const result = duration.total({ unit: "months", relativeTo });
+            expect(result).toBe(1);
+        });
+    });
 });
 
 describe("errors", () => {