diff --git a/Cargo.lock b/Cargo.lock
index 479a20aa8..5d9f9dd56 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -125,7 +125,7 @@ dependencies = [
  "serde_json",
  "syn",
  "timezone_provider",
- "zerovec 0.11.4 (git+https://github.com/unicode-org/icu4x?rev=5a56323558)",
+ "zerovec 0.11.4 (git+https://github.com/unicode-org/icu4x?rev=8262b4a)",
 ]
 
 [[package]]
@@ -168,7 +168,7 @@ dependencies = [
 [[package]]
 name = "calendrical_calculations"
 version = "0.2.2"
-source = "git+https://github.com/unicode-org/icu4x?rev=5a56323558#5a56323558fb5732046be79ef2119278ce26758e"
+source = "git+https://github.com/unicode-org/icu4x?rev=8262b4a#8262b4aafbafdbb0ebf05d21c3c680a94b852a5b"
 dependencies = [
  "core_maths",
  "displaydoc",
@@ -272,7 +272,7 @@ dependencies = [
 [[package]]
 name = "databake"
 version = "0.2.0"
-source = "git+https://github.com/unicode-org/icu4x?rev=5a56323558#5a56323558fb5732046be79ef2119278ce26758e"
+source = "git+https://github.com/unicode-org/icu4x?rev=8262b4a#8262b4aafbafdbb0ebf05d21c3c680a94b852a5b"
 dependencies = [
  "databake-derive",
  "proc-macro2",
@@ -282,7 +282,7 @@ dependencies = [
 [[package]]
 name = "databake-derive"
 version = "0.2.0"
-source = "git+https://github.com/unicode-org/icu4x?rev=5a56323558#5a56323558fb5732046be79ef2119278ce26758e"
+source = "git+https://github.com/unicode-org/icu4x?rev=8262b4a#8262b4aafbafdbb0ebf05d21c3c680a94b852a5b"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -439,47 +439,47 @@ dependencies = [
 [[package]]
 name = "icu_calendar"
 version = "2.0.4"
-source = "git+https://github.com/unicode-org/icu4x?rev=5a56323558#5a56323558fb5732046be79ef2119278ce26758e"
+source = "git+https://github.com/unicode-org/icu4x?rev=8262b4a#8262b4aafbafdbb0ebf05d21c3c680a94b852a5b"
 dependencies = [
- "calendrical_calculations 0.2.2 (git+https://github.com/unicode-org/icu4x?rev=5a56323558)",
+ "calendrical_calculations 0.2.2 (git+https://github.com/unicode-org/icu4x?rev=8262b4a)",
  "displaydoc",
  "icu_calendar_data",
  "icu_locale",
- "icu_locale_core 2.0.0 (git+https://github.com/unicode-org/icu4x?rev=5a56323558)",
+ "icu_locale_core 2.0.0 (git+https://github.com/unicode-org/icu4x?rev=8262b4a)",
  "icu_provider",
- "tinystr 0.8.1 (git+https://github.com/unicode-org/icu4x?rev=5a56323558)",
- "zerovec 0.11.4 (git+https://github.com/unicode-org/icu4x?rev=5a56323558)",
+ "tinystr 0.8.1 (git+https://github.com/unicode-org/icu4x?rev=8262b4a)",
+ "zerovec 0.11.4 (git+https://github.com/unicode-org/icu4x?rev=8262b4a)",
 ]
 
 [[package]]
 name = "icu_calendar_data"
 version = "2.0.0"
-source = "git+https://github.com/unicode-org/icu4x?rev=5a56323558#5a56323558fb5732046be79ef2119278ce26758e"
+source = "git+https://github.com/unicode-org/icu4x?rev=8262b4a#8262b4aafbafdbb0ebf05d21c3c680a94b852a5b"
 
 [[package]]
 name = "icu_collections"
 version = "2.0.0"
-source = "git+https://github.com/unicode-org/icu4x?rev=5a56323558#5a56323558fb5732046be79ef2119278ce26758e"
+source = "git+https://github.com/unicode-org/icu4x?rev=8262b4a#8262b4aafbafdbb0ebf05d21c3c680a94b852a5b"
 dependencies = [
  "displaydoc",
- "potential_utf 0.1.3 (git+https://github.com/unicode-org/icu4x?rev=5a56323558)",
- "yoke 0.8.0 (git+https://github.com/unicode-org/icu4x?rev=5a56323558)",
- "zerofrom 0.1.6 (git+https://github.com/unicode-org/icu4x?rev=5a56323558)",
- "zerovec 0.11.4 (git+https://github.com/unicode-org/icu4x?rev=5a56323558)",
+ "potential_utf 0.1.3 (git+https://github.com/unicode-org/icu4x?rev=8262b4a)",
+ "yoke 0.8.0 (git+https://github.com/unicode-org/icu4x?rev=8262b4a)",
+ "zerofrom 0.1.6 (git+https://github.com/unicode-org/icu4x?rev=8262b4a)",
+ "zerovec 0.11.4 (git+https://github.com/unicode-org/icu4x?rev=8262b4a)",
 ]
 
 [[package]]
 name = "icu_locale"
 version = "2.0.0"
-source = "git+https://github.com/unicode-org/icu4x?rev=5a56323558#5a56323558fb5732046be79ef2119278ce26758e"
+source = "git+https://github.com/unicode-org/icu4x?rev=8262b4a#8262b4aafbafdbb0ebf05d21c3c680a94b852a5b"
 dependencies = [
  "icu_collections",
- "icu_locale_core 2.0.0 (git+https://github.com/unicode-org/icu4x?rev=5a56323558)",
+ "icu_locale_core 2.0.0 (git+https://github.com/unicode-org/icu4x?rev=8262b4a)",
  "icu_locale_data",
  "icu_provider",
- "potential_utf 0.1.3 (git+https://github.com/unicode-org/icu4x?rev=5a56323558)",
- "tinystr 0.8.1 (git+https://github.com/unicode-org/icu4x?rev=5a56323558)",
- "zerovec 0.11.4 (git+https://github.com/unicode-org/icu4x?rev=5a56323558)",
+ "potential_utf 0.1.3 (git+https://github.com/unicode-org/icu4x?rev=8262b4a)",
+ "tinystr 0.8.1 (git+https://github.com/unicode-org/icu4x?rev=8262b4a)",
+ "zerovec 0.11.4 (git+https://github.com/unicode-org/icu4x?rev=8262b4a)",
 ]
 
 [[package]]
@@ -497,35 +497,35 @@ dependencies = [
 [[package]]
 name = "icu_locale_core"
 version = "2.0.0"
-source = "git+https://github.com/unicode-org/icu4x?rev=5a56323558#5a56323558fb5732046be79ef2119278ce26758e"
+source = "git+https://github.com/unicode-org/icu4x?rev=8262b4a#8262b4aafbafdbb0ebf05d21c3c680a94b852a5b"
 dependencies = [
  "displaydoc",
- "litemap 0.8.0 (git+https://github.com/unicode-org/icu4x?rev=5a56323558)",
+ "litemap 0.8.0 (git+https://github.com/unicode-org/icu4x?rev=8262b4a)",
  "serde",
- "tinystr 0.8.1 (git+https://github.com/unicode-org/icu4x?rev=5a56323558)",
- "writeable 0.6.1 (git+https://github.com/unicode-org/icu4x?rev=5a56323558)",
- "zerovec 0.11.4 (git+https://github.com/unicode-org/icu4x?rev=5a56323558)",
+ "tinystr 0.8.1 (git+https://github.com/unicode-org/icu4x?rev=8262b4a)",
+ "writeable 0.6.1 (git+https://github.com/unicode-org/icu4x?rev=8262b4a)",
+ "zerovec 0.11.4 (git+https://github.com/unicode-org/icu4x?rev=8262b4a)",
 ]
 
 [[package]]
 name = "icu_locale_data"
 version = "2.0.0"
-source = "git+https://github.com/unicode-org/icu4x?rev=5a56323558#5a56323558fb5732046be79ef2119278ce26758e"
+source = "git+https://github.com/unicode-org/icu4x?rev=8262b4a#8262b4aafbafdbb0ebf05d21c3c680a94b852a5b"
 
 [[package]]
 name = "icu_provider"
 version = "2.0.0"
-source = "git+https://github.com/unicode-org/icu4x?rev=5a56323558#5a56323558fb5732046be79ef2119278ce26758e"
+source = "git+https://github.com/unicode-org/icu4x?rev=8262b4a#8262b4aafbafdbb0ebf05d21c3c680a94b852a5b"
 dependencies = [
  "displaydoc",
- "icu_locale_core 2.0.0 (git+https://github.com/unicode-org/icu4x?rev=5a56323558)",
+ "icu_locale_core 2.0.0 (git+https://github.com/unicode-org/icu4x?rev=8262b4a)",
  "serde",
  "stable_deref_trait",
- "writeable 0.6.1 (git+https://github.com/unicode-org/icu4x?rev=5a56323558)",
- "yoke 0.8.0 (git+https://github.com/unicode-org/icu4x?rev=5a56323558)",
- "zerofrom 0.1.6 (git+https://github.com/unicode-org/icu4x?rev=5a56323558)",
+ "writeable 0.6.1 (git+https://github.com/unicode-org/icu4x?rev=8262b4a)",
+ "yoke 0.8.0 (git+https://github.com/unicode-org/icu4x?rev=8262b4a)",
+ "zerofrom 0.1.6 (git+https://github.com/unicode-org/icu4x?rev=8262b4a)",
  "zerotrie",
- "zerovec 0.11.4 (git+https://github.com/unicode-org/icu4x?rev=5a56323558)",
+ "zerovec 0.11.4 (git+https://github.com/unicode-org/icu4x?rev=8262b4a)",
 ]
 
 [[package]]
@@ -568,7 +568,7 @@ checksum = "4a5f13b858c8d314ee3e8f639011f7ccefe71f97f96e50151fb991f267928e2c"
 [[package]]
 name = "ixdtf"
 version = "0.6.3"
-source = "git+https://github.com/unicode-org/icu4x?rev=5a56323558#5a56323558fb5732046be79ef2119278ce26758e"
+source = "git+https://github.com/unicode-org/icu4x?rev=8262b4a#8262b4aafbafdbb0ebf05d21c3c680a94b852a5b"
 
 [[package]]
 name = "jiff-tzdb"
@@ -607,7 +607,7 @@ checksum = "241eaef5fd12c88705a01fc1066c48c4b36e0dd4377dcdc7ec3942cea7a69956"
 [[package]]
 name = "litemap"
 version = "0.8.0"
-source = "git+https://github.com/unicode-org/icu4x?rev=5a56323558#5a56323558fb5732046be79ef2119278ce26758e"
+source = "git+https://github.com/unicode-org/icu4x?rev=8262b4a#8262b4aafbafdbb0ebf05d21c3c680a94b852a5b"
 dependencies = [
  "serde_core",
 ]
@@ -660,11 +660,11 @@ checksum = "84df19adbe5b5a0782edcab45899906947ab039ccf4573713735ee7de1e6b08a"
 [[package]]
 name = "potential_utf"
 version = "0.1.3"
-source = "git+https://github.com/unicode-org/icu4x?rev=5a56323558#5a56323558fb5732046be79ef2119278ce26758e"
+source = "git+https://github.com/unicode-org/icu4x?rev=8262b4a#8262b4aafbafdbb0ebf05d21c3c680a94b852a5b"
 dependencies = [
  "serde_core",
- "writeable 0.6.1 (git+https://github.com/unicode-org/icu4x?rev=5a56323558)",
- "zerovec 0.11.4 (git+https://github.com/unicode-org/icu4x?rev=5a56323558)",
+ "writeable 0.6.1 (git+https://github.com/unicode-org/icu4x?rev=8262b4a)",
+ "zerovec 0.11.4 (git+https://github.com/unicode-org/icu4x?rev=8262b4a)",
 ]
 
 [[package]]
@@ -870,7 +870,7 @@ dependencies = [
  "num-traits",
  "temporal_rs",
  "timezone_provider",
- "writeable 0.6.1 (git+https://github.com/unicode-org/icu4x?rev=5a56323558)",
+ "writeable 0.6.1 (git+https://github.com/unicode-org/icu4x?rev=8262b4a)",
  "zoneinfo64",
 ]
 
@@ -887,9 +887,9 @@ dependencies = [
  "num-traits",
  "resb",
  "timezone_provider",
- "tinystr 0.8.1 (git+https://github.com/unicode-org/icu4x?rev=5a56323558)",
+ "tinystr 0.8.1 (git+https://github.com/unicode-org/icu4x?rev=8262b4a)",
  "web-time",
- "writeable 0.6.1 (git+https://github.com/unicode-org/icu4x?rev=5a56323558)",
+ "writeable 0.6.1 (git+https://github.com/unicode-org/icu4x?rev=8262b4a)",
  "zoneinfo64",
 ]
 
@@ -902,11 +902,11 @@ dependencies = [
  "jiff-tzdb",
  "serde",
  "serde_json",
- "tinystr 0.8.1 (git+https://github.com/unicode-org/icu4x?rev=5a56323558)",
+ "tinystr 0.8.1 (git+https://github.com/unicode-org/icu4x?rev=8262b4a)",
  "tzif",
  "yoke 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "zerotrie",
- "zerovec 0.11.4 (git+https://github.com/unicode-org/icu4x?rev=5a56323558)",
+ "zerovec 0.11.4 (git+https://github.com/unicode-org/icu4x?rev=8262b4a)",
  "zoneinfo64",
  "zoneinfo_rs",
 ]
@@ -924,12 +924,12 @@ dependencies = [
 [[package]]
 name = "tinystr"
 version = "0.8.1"
-source = "git+https://github.com/unicode-org/icu4x?rev=5a56323558#5a56323558fb5732046be79ef2119278ce26758e"
+source = "git+https://github.com/unicode-org/icu4x?rev=8262b4a#8262b4aafbafdbb0ebf05d21c3c680a94b852a5b"
 dependencies = [
  "databake",
  "displaydoc",
  "serde_core",
- "zerovec 0.11.4 (git+https://github.com/unicode-org/icu4x?rev=5a56323558)",
+ "zerovec 0.11.4 (git+https://github.com/unicode-org/icu4x?rev=8262b4a)",
 ]
 
 [[package]]
@@ -1234,7 +1234,7 @@ checksum = "ea2f10b9bb0928dfb1b42b65e1f9e36f7f54dbdf08457afefb38afcdec4fa2bb"
 [[package]]
 name = "writeable"
 version = "0.6.1"
-source = "git+https://github.com/unicode-org/icu4x?rev=5a56323558#5a56323558fb5732046be79ef2119278ce26758e"
+source = "git+https://github.com/unicode-org/icu4x?rev=8262b4a#8262b4aafbafdbb0ebf05d21c3c680a94b852a5b"
 
 [[package]]
 name = "yoke"
@@ -1251,11 +1251,11 @@ dependencies = [
 [[package]]
 name = "yoke"
 version = "0.8.0"
-source = "git+https://github.com/unicode-org/icu4x?rev=5a56323558#5a56323558fb5732046be79ef2119278ce26758e"
+source = "git+https://github.com/unicode-org/icu4x?rev=8262b4a#8262b4aafbafdbb0ebf05d21c3c680a94b852a5b"
 dependencies = [
  "stable_deref_trait",
- "yoke-derive 0.8.0 (git+https://github.com/unicode-org/icu4x?rev=5a56323558)",
- "zerofrom 0.1.6 (git+https://github.com/unicode-org/icu4x?rev=5a56323558)",
+ "yoke-derive 0.8.0 (git+https://github.com/unicode-org/icu4x?rev=8262b4a)",
+ "zerofrom 0.1.6 (git+https://github.com/unicode-org/icu4x?rev=8262b4a)",
 ]
 
 [[package]]
@@ -1273,7 +1273,7 @@ dependencies = [
 [[package]]
 name = "yoke-derive"
 version = "0.8.0"
-source = "git+https://github.com/unicode-org/icu4x?rev=5a56323558#5a56323558fb5732046be79ef2119278ce26758e"
+source = "git+https://github.com/unicode-org/icu4x?rev=8262b4a#8262b4aafbafdbb0ebf05d21c3c680a94b852a5b"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -1293,9 +1293,9 @@ dependencies = [
 [[package]]
 name = "zerofrom"
 version = "0.1.6"
-source = "git+https://github.com/unicode-org/icu4x?rev=5a56323558#5a56323558fb5732046be79ef2119278ce26758e"
+source = "git+https://github.com/unicode-org/icu4x?rev=8262b4a#8262b4aafbafdbb0ebf05d21c3c680a94b852a5b"
 dependencies = [
- "zerofrom-derive 0.1.6 (git+https://github.com/unicode-org/icu4x?rev=5a56323558)",
+ "zerofrom-derive 0.1.6 (git+https://github.com/unicode-org/icu4x?rev=8262b4a)",
 ]
 
 [[package]]
@@ -1313,7 +1313,7 @@ dependencies = [
 [[package]]
 name = "zerofrom-derive"
 version = "0.1.6"
-source = "git+https://github.com/unicode-org/icu4x?rev=5a56323558#5a56323558fb5732046be79ef2119278ce26758e"
+source = "git+https://github.com/unicode-org/icu4x?rev=8262b4a#8262b4aafbafdbb0ebf05d21c3c680a94b852a5b"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -1324,13 +1324,13 @@ dependencies = [
 [[package]]
 name = "zerotrie"
 version = "0.2.2"
-source = "git+https://github.com/unicode-org/icu4x?rev=5a56323558#5a56323558fb5732046be79ef2119278ce26758e"
+source = "git+https://github.com/unicode-org/icu4x?rev=8262b4a#8262b4aafbafdbb0ebf05d21c3c680a94b852a5b"
 dependencies = [
  "databake",
  "displaydoc",
- "litemap 0.8.0 (git+https://github.com/unicode-org/icu4x?rev=5a56323558)",
+ "litemap 0.8.0 (git+https://github.com/unicode-org/icu4x?rev=8262b4a)",
  "serde_core",
- "zerovec 0.11.4 (git+https://github.com/unicode-org/icu4x?rev=5a56323558)",
+ "zerovec 0.11.4 (git+https://github.com/unicode-org/icu4x?rev=8262b4a)",
 ]
 
 [[package]]
@@ -1345,19 +1345,19 @@ dependencies = [
 [[package]]
 name = "zerovec"
 version = "0.11.4"
-source = "git+https://github.com/unicode-org/icu4x?rev=5a56323558#5a56323558fb5732046be79ef2119278ce26758e"
+source = "git+https://github.com/unicode-org/icu4x?rev=8262b4a#8262b4aafbafdbb0ebf05d21c3c680a94b852a5b"
 dependencies = [
  "databake",
  "serde",
- "yoke 0.8.0 (git+https://github.com/unicode-org/icu4x?rev=5a56323558)",
- "zerofrom 0.1.6 (git+https://github.com/unicode-org/icu4x?rev=5a56323558)",
+ "yoke 0.8.0 (git+https://github.com/unicode-org/icu4x?rev=8262b4a)",
+ "zerofrom 0.1.6 (git+https://github.com/unicode-org/icu4x?rev=8262b4a)",
  "zerovec-derive",
 ]
 
 [[package]]
 name = "zerovec-derive"
 version = "0.11.1"
-source = "git+https://github.com/unicode-org/icu4x?rev=5a56323558#5a56323558fb5732046be79ef2119278ce26758e"
+source = "git+https://github.com/unicode-org/icu4x?rev=8262b4a#8262b4aafbafdbb0ebf05d21c3c680a94b852a5b"
 dependencies = [
  "proc-macro2",
  "quote",
diff --git a/Cargo.toml b/Cargo.toml
index e3a342ee4..a41a30b60 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -34,22 +34,22 @@ timezone_provider = { version = "~0.1.0", path = "./provider" }
 zoneinfo_rs = { version = "~0.0.17", path = "./zoneinfo" }
 
 # Dependencies
-tinystr = { git = "https://github.com/unicode-org/icu4x", rev = "5a56323558" }
-icu_calendar = { git = "https://github.com/unicode-org/icu4x", rev = "5a56323558", default-features = false }
-icu_locale = { git = "https://github.com/unicode-org/icu4x", rev = "5a56323558" }
+tinystr = { git = "https://github.com/unicode-org/icu4x", rev = "8262b4a" }
+icu_calendar = { git = "https://github.com/unicode-org/icu4x", rev = "8262b4a", default-features = false }
+icu_locale = { git = "https://github.com/unicode-org/icu4x", rev = "8262b4a" }
 rustc-hash = "2.1.0"
 num-traits = { version = "0.2.19", default-features = false }
-ixdtf = { git = "https://github.com/unicode-org/icu4x", rev = "5a56323558" }
+ixdtf = { git = "https://github.com/unicode-org/icu4x", rev = "8262b4a" }
 iana-time-zone = "0.1.64"
 log = "0.4.28"
 tzif = "0.4.0"
 jiff-tzdb = "0.1.4"
 combine = "4.6.7"
 web-time = "1.1.0"
-zerovec = { git = "https://github.com/unicode-org/icu4x", rev = "5a56323558" }
-databake = { git = "https://github.com/unicode-org/icu4x", rev = "5a56323558" }
-zerotrie = { git = "https://github.com/unicode-org/icu4x", rev = "5a56323558" }
-writeable = { git = "https://github.com/unicode-org/icu4x", rev = "5a56323558" }
+zerovec = { git = "https://github.com/unicode-org/icu4x", rev = "8262b4a" }
+databake = { git = "https://github.com/unicode-org/icu4x", rev = "8262b4a" }
+zerotrie = { git = "https://github.com/unicode-org/icu4x", rev = "8262b4a" }
+writeable = { git = "https://github.com/unicode-org/icu4x", rev = "8262b4a" }
 zoneinfo64 = "0.2.0"
 
 # Diplomat
diff --git a/src/builtins/core/calendar.rs b/src/builtins/core/calendar.rs
index 50296ed7c..ddb30c407 100644
--- a/src/builtins/core/calendar.rs
+++ b/src/builtins/core/calendar.rs
@@ -7,6 +7,7 @@ use crate::{
     builtins::core::{
         duration::DateDuration, Duration, PlainDate, PlainDateTime, PlainMonthDay, PlainYearMonth,
     },
+    error::ErrorMessage,
     iso::IsoDate,
     options::{Overflow, Unit},
     parsers::parse_allowed_calendar_formats,
@@ -24,8 +25,13 @@ use icu_calendar::{
 };
 use icu_calendar::{
     cal::{HijriTabularEpoch, HijriTabularLeapYears},
-    options::{DateFromFieldsOptions, MissingFieldsStrategy, Overflow as IcuOverflow},
+    options::{
+        DateAddOptions, DateDifferenceOptions, DateFromFieldsOptions, MissingFieldsStrategy,
+        Overflow as IcuOverflow,
+    },
     preferences::CalendarAlgorithm,
+    types::DateDuration as IcuDateDuration,
+    types::DateDurationUnit as IcuUnit,
     types::DateFields,
     types::MonthCode as IcuMonthCode,
     Gregorian,
@@ -217,6 +223,22 @@ impl From<Overflow> for IcuOverflow {
     }
 }
 
+impl TryFrom<Unit> for IcuUnit {
+    type Error = TemporalError;
+    fn try_from(other: Unit) -> TemporalResult<Self> {
+        Ok(match other {
+            Unit::Day => IcuUnit::Days,
+            Unit::Week => IcuUnit::Weeks,
+            Unit::Month => IcuUnit::Months,
+            Unit::Year => IcuUnit::Years,
+            _ => {
+                return Err(TemporalError::r#type()
+                    .with_message("Found time unit when computing CalendarDateUntil."))
+            }
+        })
+    }
+}
+
 impl<'a> TryFrom<&'a CalendarFields> for DateFields<'a> {
     type Error = TemporalError;
     fn try_from(other: &'a CalendarFields) -> TemporalResult<Self> {
@@ -419,7 +441,32 @@ impl Calendar {
             return PlainDate::try_new(result.year, result.month, result.day, self.clone());
         }
 
-        Err(TemporalError::range().with_message("Not yet implemented."))
+        // This should be a valid duration at this point so we can just call .abs()
+        let invalid = TemporalError::range().with_enum(ErrorMessage::DurationNotValid);
+        let duration = IcuDateDuration {
+            is_negative: duration.years < 0
+                || duration.months < 0
+                || duration.weeks < 0
+                || duration.days < 0,
+            years: u32::try_from(duration.years.abs()).map_err(|_| invalid)?,
+            months: u32::try_from(duration.months.abs()).map_err(|_| invalid)?,
+            weeks: u32::try_from(duration.weeks.abs()).map_err(|_| invalid)?,
+            days: u64::try_from(duration.days.abs()).map_err(|_| invalid)?,
+        };
+        let mut options = DateAddOptions::default();
+        options.overflow = Some(overflow.into());
+        let calendar_date = self.0.from_iso(*date.to_icu4x().inner());
+
+        let added = self.0.add(&calendar_date, duration, options)?;
+
+        let iso = self.0.to_iso(&added);
+        PlainDate::new_with_overflow(
+            Iso.extended_year(&iso),
+            Iso.month(&iso).ordinal,
+            Iso.day_of_month(&iso).0,
+            self.clone(),
+            overflow,
+        )
     }
 
     /// `CalendarDateUntil`
@@ -433,7 +480,24 @@ impl Calendar {
             let date_duration = one.diff_iso_date(two, largest_unit)?;
             return Ok(Duration::from(date_duration));
         }
-        Err(TemporalError::range().with_message("Not yet implemented."))
+        let mut options = DateDifferenceOptions::default();
+        options.largest_unit = Some(largest_unit.try_into()?);
+        let calendar_date1 = self.0.from_iso(*one.to_icu4x().inner());
+        let calendar_date2 = self.0.from_iso(*two.to_icu4x().inner());
+
+        let added = self.0.until(&calendar_date1, &calendar_date2, options)?;
+
+        let days = added
+            .days
+            .try_into()
+            .map_err(|_| TemporalError::range().with_enum(ErrorMessage::DurationNotValid))?;
+        let duration = DateDuration::new(
+            added.years.into(),
+            added.months.into(),
+            added.weeks.into(),
+            days,
+        )?;
+        Ok(Duration::from(duration))
     }
 
     /// `CalendarEra`
diff --git a/src/builtins/core/duration.rs b/src/builtins/core/duration.rs
index fc19e7912..efc63106c 100644
--- a/src/builtins/core/duration.rs
+++ b/src/builtins/core/duration.rs
@@ -636,7 +636,7 @@ impl Duration {
             microseconds,
             nanoseconds,
         ) {
-            return Err(TemporalError::range().with_message("Duration was not valid."));
+            return Err(TemporalError::range().with_enum(ErrorMessage::DurationNotValid));
         }
         let sign = duration_sign(&[
             years,
diff --git a/src/error.rs b/src/error.rs
index 9ea0623ae..0e5847477 100644
--- a/src/error.rs
+++ b/src/error.rs
@@ -4,7 +4,7 @@ use core::fmt;
 use ixdtf::ParseError;
 use timezone_provider::TimeZoneProviderError;
 
-use icu_calendar::DateError;
+use icu_calendar::{cal::AnyCalendarDifferenceError, DateError};
 
 /// `TemporalError`'s error type.
 #[derive(Debug, Default, Clone, Copy, PartialEq)]
@@ -158,6 +158,12 @@ impl From<DateError> for TemporalError {
     }
 }
 
+impl From<AnyCalendarDifferenceError> for TemporalError {
+    fn from(error: AnyCalendarDifferenceError) -> Self {
+        TemporalError::range().with_enum(ErrorMessage::Icu4xUntil(error))
+    }
+}
+
 impl From<ParseError> for TemporalError {
     fn from(error: ParseError) -> Self {
         TemporalError::range().with_enum(ErrorMessage::Ixdtf(error))
@@ -173,6 +179,7 @@ pub(crate) enum ErrorMessage {
     ZDTOutOfDayBounds,
     LargestUnitCannotBeDateUnit,
     DateOutOfRange,
+    DurationNotValid,
 
     // Numerical errors
     NumberNotFinite,
@@ -211,6 +218,7 @@ pub(crate) enum ErrorMessage {
     String(&'static str),
     Ixdtf(ParseError),
     Icu4xDate(DateError),
+    Icu4xUntil(AnyCalendarDifferenceError),
 }
 
 impl ErrorMessage {
@@ -223,6 +231,7 @@ impl ErrorMessage {
             Self::ZDTOutOfDayBounds => "ZonedDateTime is outside the expected day bounds",
             Self::LargestUnitCannotBeDateUnit => "Largest unit cannot be a date unit",
             Self::DateOutOfRange => "Date is not within ISO date time limits.",
+            Self::DurationNotValid => "Duration was not valid.",
             Self::NumberNotFinite => "number value is not a finite value.",
             Self::NumberNotIntegral => "value must be integral.",
             Self::NumberNotPositive => "integer must be positive.",
@@ -267,6 +276,10 @@ impl ErrorMessage {
             Self::Icu4xDate(DateError::InconsistentMonth) => "Inconsistent month/monthCode.",
             Self::Icu4xDate(DateError::NotEnoughFields) => "Insufficient fields.",
             Self::Icu4xDate(_) => "Date error.",
+            Self::Icu4xUntil(AnyCalendarDifferenceError::MismatchedCalendars) => {
+                "Mismatched calendars."
+            }
+            Self::Icu4xUntil(_) => "Arithmetic error.",
         }
     }
 }