diff --git a/src/duration.ts b/src/duration.ts
index 58492b2..82b531d 100644
--- a/src/duration.ts
+++ b/src/duration.ts
@@ -104,27 +104,80 @@ export function applyDuration(date: Date | number, duration: Duration): Date {
   return r
 }
 
-export function elapsedTime(date: Date, precision: Unit = 'second', now = Date.now()): Duration {
-  const delta = date.getTime() - now
-  if (delta === 0) return new Duration()
-  const sign = Math.sign(delta)
-  const ms = Math.abs(delta)
-  const sec = Math.floor(ms / 1000)
-  const min = Math.floor(sec / 60)
-  const hr = Math.floor(min / 60)
-  const day = Math.floor(hr / 24)
-  const month = Math.floor(day / 30)
-  const year = Math.floor(month / 12)
-  const i = unitNames.indexOf(precision) || unitNames.length
+// Calculates the elapsed time from `now` to `date`.
+export function elapsedTime(
+  date: Date,
+  precision: Unit = 'second',
+  nowTimestamp: Date | number = Date.now(),
+): Duration {
+  const now = new Date(nowTimestamp)
+  // eslint-disable-next-line prefer-const
+  let [sign, subtrahend, minuend] = date < now ? [-1, now, date] : [1, date, now]
+  let ms: number
+  let sec: number
+  let min: number
+  let hr: number
+  let day: number
+  let month: number
+  let year: number
+  // Using UTC to avoid timezone-specific variations.
+  if (subtrahend.getUTCMilliseconds() >= minuend.getUTCMilliseconds()) {
+    ms = subtrahend.getUTCMilliseconds() - minuend.getUTCMilliseconds()
+  } else {
+    ms = 1000 + subtrahend.getUTCMilliseconds() - minuend.getUTCMilliseconds()
+    subtrahend = new Date(subtrahend.getTime() - 1000)
+  }
+
+  if (subtrahend.getUTCSeconds() >= minuend.getUTCSeconds()) {
+    sec = subtrahend.getUTCSeconds() - minuend.getUTCSeconds()
+  } else {
+    sec = 60 + subtrahend.getUTCSeconds() - minuend.getUTCSeconds()
+    subtrahend = new Date(subtrahend.getTime() - 1000 * 60)
+  }
+
+  if (subtrahend.getUTCMinutes() >= minuend.getUTCMinutes()) {
+    min = subtrahend.getUTCMinutes() - minuend.getUTCMinutes()
+  } else {
+    min = 60 + subtrahend.getUTCMinutes() - minuend.getUTCMinutes()
+    subtrahend = new Date(subtrahend.getTime() - 1000 * 60 * 60)
+  }
+
+  if (subtrahend.getUTCHours() >= minuend.getUTCHours()) {
+    hr = subtrahend.getUTCHours() - minuend.getUTCHours()
+  } else {
+    hr = 24 + subtrahend.getUTCHours() - minuend.getUTCHours()
+    subtrahend = new Date(subtrahend.getTime() - 1000 * 60 * 60 * 24)
+  }
+
+  if (subtrahend.getUTCDate() >= minuend.getUTCDate()) {
+    day = subtrahend.getUTCDate() - minuend.getUTCDate()
+  } else {
+    day = subtrahend.getUTCDate()
+    subtrahend = new Date(subtrahend.getTime() - 1000 * 60 * 60 * 24 * day)
+    day += Math.max(0, subtrahend.getUTCDate() - minuend.getUTCDate())
+  }
+
+  year = subtrahend.getUTCFullYear() - minuend.getUTCFullYear()
+  if (subtrahend.getUTCMonth() >= minuend.getUTCMonth()) {
+    month = subtrahend.getUTCMonth() - minuend.getUTCMonth()
+  } else {
+    month = 12 + subtrahend.getUTCMonth() - minuend.getUTCMonth()
+    year -= 1
+  }
+
+  let precisionIndex = unitNames.indexOf(precision)
+  if (precisionIndex === -1) {
+    precisionIndex = unitNames.length
+  }
   return new Duration(
-    i >= 0 ? year * sign : 0,
-    i >= 1 ? (month - year * 12) * sign : 0,
+    precisionIndex >= 0 ? year * sign : 0,
+    precisionIndex >= 1 ? month * sign : 0,
     0,
-    i >= 3 ? (day - month * 30) * sign : 0,
-    i >= 4 ? (hr - day * 24) * sign : 0,
-    i >= 5 ? (min - hr * 60) * sign : 0,
-    i >= 6 ? (sec - min * 60) * sign : 0,
-    i >= 7 ? (ms - sec * 1000) * sign : 0,
+    precisionIndex >= 3 ? day * sign : 0,
+    precisionIndex >= 4 ? hr * sign : 0,
+    precisionIndex >= 5 ? min * sign : 0,
+    precisionIndex >= 6 ? sec * sign : 0,
+    precisionIndex >= 7 ? ms * sign : 0,
   )
 }
 
diff --git a/test/duration.ts b/test/duration.ts
index ecb9e68..f5e2e0e 100644
--- a/test/duration.ts
+++ b/test/duration.ts
@@ -101,130 +101,244 @@ suite('duration', function () {
   })
 
   suite('elapsedTime', function () {
-    const elapsed = new Set([
+    const elapsedTests = [
       {
         now: '2022-01-21T16:48:44.104Z',
-        input: '2022-10-21T16:48:44.104Z',
-        expected: 'P9M3D',
+        input: '2022-01-21T16:48:45.104Z',
+        expected: 'PT1S',
       },
       {
         now: '2022-01-21T16:48:44.104Z',
-        input: '2022-10-21T16:48:45.104Z',
-        expected: 'P9M3DT1S',
+        input: '2022-01-21T16:49:43.104Z',
+        expected: 'PT59S',
       },
       {
         now: '2022-01-21T16:48:44.104Z',
-        input: '2022-10-21T16:48:45.104Z',
-        precision: 'day',
-        expected: 'P9M3D',
+        input: '2022-01-21T16:49:44.104Z',
+        expected: 'PT1M',
       },
       {
-        now: '2022-10-21T16:44:44.104Z',
-        input: '2022-10-21T16:48:44.104Z',
-        expected: 'PT4M',
+        now: '2022-01-21T16:48:44.104Z',
+        input: '2022-01-21T16:49:46.104Z',
+        expected: 'PT1M2S',
       },
       {
-        now: '2022-09-22T16:48:44.104Z',
-        input: '2022-10-21T16:48:44.104Z',
-        expected: 'P29D',
+        now: '2022-01-21T16:48:44.104Z',
+        input: '2022-01-21T17:47:43.104Z',
+        expected: 'PT58M59S',
       },
       {
-        now: '2022-10-24T14:46:00.000Z',
-        input: '2022-10-24T14:46:10.000Z',
-        expected: 'PT10S',
+        now: '2022-01-21T16:48:44.104Z',
+        input: '2022-01-21T17:48:44.104Z',
+        expected: 'PT1H',
       },
       {
-        now: '2022-10-24T14:46:00.000Z',
-        input: '2022-10-24T14:45:50.000Z',
-        expected: '-PT10S',
+        now: '2022-01-21T16:48:44.104Z',
+        input: '2022-01-21T17:50:47.104Z',
+        expected: 'PT1H2M3S',
       },
       {
-        now: '2022-10-24T14:46:00.000Z',
-        input: '2022-10-24T14:45:50.000Z',
-        precision: 'minute',
-        expected: 'PT0M',
+        now: '2022-01-21T16:48:44.104Z',
+        input: '2022-01-22T15:47:43.104Z',
+        expected: 'PT22H58M59S',
       },
       {
-        now: '2022-10-24T14:46:00.000Z',
-        input: '2022-10-24T14:47:40.000Z',
-        expected: 'PT1M40S',
+        now: '2022-01-21T16:48:44.104Z',
+        input: '2022-01-22T16:48:44.104Z',
+        expected: 'P1D',
       },
       {
-        now: '2022-10-24T14:46:00.000Z',
-        input: '2022-10-24T14:44:20.000Z',
-        expected: '-PT1M40S',
+        now: '2022-01-21T16:48:44.104Z',
+        input: '2022-01-22T18:51:48.104Z',
+        expected: 'P1DT2H3M4S',
       },
       {
-        now: '2022-10-24T14:46:00.000Z',
-        input: '2022-10-24T14:44:20.000Z',
-        precision: 'minute',
-        expected: '-PT1M',
+        now: '2022-01-21T16:48:44.104Z',
+        input: '2022-02-20T15:47:43.104Z',
+        expected: 'P29DT22H58M59S',
       },
       {
-        now: '2022-10-24T14:46:00.000Z',
-        input: '2022-10-24T15:51:40.000Z',
-        expected: 'PT1H5M40S',
+        now: '2022-01-21T16:48:44.104Z',
+        input: '2022-02-21T16:48:44.104Z',
+        expected: 'P1M',
       },
       {
-        now: '2022-10-24T14:46:00.000Z',
-        input: '2022-10-24T15:51:40.000Z',
-        precision: 'minute',
-        expected: 'PT1H5M',
+        now: '2022-01-21T16:48:44.104Z',
+        input: '2022-02-23T19:52:49.104Z',
+        expected: 'P1M2DT3H4M5S',
       },
       {
-        now: '2022-10-24T14:46:00.000Z',
-        input: '2022-10-24T15:52:00.000Z',
-        expected: 'PT1H6M',
+        now: '2022-02-21T16:48:44.104Z',
+        input: '2023-01-20T15:47:43.104Z',
+        expected: 'P10M29DT22H58M59S',
       },
       {
-        now: '2022-10-24T14:46:00.000Z',
-        input: '2022-10-24T17:46:00.000Z',
-        expected: 'PT3H',
+        now: '2022-01-21T16:48:44.104Z',
+        input: '2023-01-21T16:48:44.104Z',
+        expected: 'P1Y',
+      },
+      {
+        now: '2022-01-21T16:48:44.104Z',
+        input: '2023-03-24T20:53:50.104Z',
+        expected: 'P1Y2M3DT4H5M6S',
       },
+
       {
-        now: '2022-10-24T14:46:00.000Z',
-        input: '2022-10-24T10:46:00.000Z',
-        expected: '-PT4H',
+        now: '2022-01-21T16:48:44.104Z',
+        input: '2023-03-24T20:53:50.104Z',
+        precision: 'second',
+        expected: 'P1Y2M3DT4H5M6S',
       },
       {
-        now: '2022-10-24T14:46:00.000Z',
-        input: '2022-10-25T18:46:00.000Z',
-        expected: 'P1DT4H',
+        now: '2022-01-21T16:48:44.104Z',
+        input: '2023-03-24T20:53:50.104Z',
+        precision: 'minute',
+        expected: 'P1Y2M3DT4H5M',
       },
       {
-        now: '2022-10-24T14:46:00.000Z',
-        input: '2022-10-23T10:46:00.000Z',
-        expected: '-P1DT4H',
+        now: '2022-01-21T16:48:44.104Z',
+        input: '2023-03-24T20:53:50.104Z',
+        precision: 'hour',
+        expected: 'P1Y2M3DT4H',
       },
       {
-        now: '2022-10-24T14:46:00.000Z',
-        input: '2022-10-23T10:46:00.000Z',
+        now: '2022-01-21T16:48:44.104Z',
+        input: '2023-03-24T20:53:50.104Z',
         precision: 'day',
+        expected: 'P1Y2M3D',
+      },
+      {
+        now: '2022-01-21T16:48:44.104Z',
+        input: '2023-03-24T20:53:50.104Z',
+        precision: 'month',
+        expected: 'P1Y2M',
+      },
+      {
+        now: '2022-01-21T16:48:44.104Z',
+        input: '2023-03-24T20:53:50.104Z',
+        precision: 'year',
+        expected: 'P1Y',
+      },
+      {
+        now: '2022-01-21T16:48:44.104Z',
+        input: '2023-03-24T20:53:50.104Z',
+        precision: 'garbage',
+        expected: 'P1Y2M3DT4H5M6S',
+      },
+
+      {
+        now: '2022-01-21T16:48:45.104Z',
+        input: '2022-01-21T16:48:44.104Z',
+        expected: '-PT1S',
+      },
+      {
+        now: '2022-01-21T16:49:43.104Z',
+        input: '2022-01-21T16:48:44.104Z',
+        expected: '-PT59S',
+      },
+      {
+        now: '2022-01-21T16:49:44.104Z',
+        input: '2022-01-21T16:48:44.104Z',
+        expected: '-PT1M',
+      },
+      {
+        now: '2022-01-21T16:49:46.104Z',
+        input: '2022-01-21T16:48:44.104Z',
+        expected: '-PT1M2S',
+      },
+      {
+        now: '2022-01-21T17:47:43.104Z',
+        input: '2022-01-21T16:48:44.104Z',
+        expected: '-PT58M59S',
+      },
+      {
+        now: '2022-01-21T17:48:44.104Z',
+        input: '2022-01-21T16:48:44.104Z',
+        expected: '-PT1H',
+      },
+      {
+        now: '2022-01-21T17:50:47.104Z',
+        input: '2022-01-21T16:48:44.104Z',
+        expected: '-PT1H2M3S',
+      },
+      {
+        now: '2022-01-22T15:47:43.104Z',
+        input: '2022-01-21T16:48:44.104Z',
+        expected: '-PT22H58M59S',
+      },
+      {
+        now: '2022-01-22T16:48:44.104Z',
+        input: '2022-01-21T16:48:44.104Z',
         expected: '-P1D',
       },
       {
-        now: '2022-10-24T14:46:00.000Z',
-        input: '2021-10-30T14:46:00.000Z',
-        expected: '-P11M29D',
+        now: '2022-01-22T18:51:48.104Z',
+        input: '2022-01-21T16:48:44.104Z',
+        expected: '-P1DT2H3M4S',
       },
       {
-        now: '2022-10-24T14:46:00.000Z',
-        input: '2021-10-30T14:46:00.000Z',
-        precision: 'month',
-        expected: '-P11M',
+        now: '2022-02-20T15:47:43.104Z',
+        input: '2022-01-21T16:48:44.104Z',
+        expected: '-P29DT22H58M59S',
+      },
+      {
+        now: '2022-02-21T16:48:44.104Z',
+        input: '2022-01-21T16:48:44.104Z',
+        expected: '-P1M',
+      },
+      {
+        now: '2022-02-23T19:52:49.104Z',
+        input: '2022-01-21T16:48:44.104Z',
+        expected: '-P1M2DT3H4M5S',
+      },
+      {
+        now: '2023-01-20T15:47:43.104Z',
+        input: '2022-02-21T16:48:44.104Z',
+        expected: '-P10M29DT22H58M59S',
       },
       {
-        now: '2022-10-24T14:46:00.000Z',
-        input: '2021-10-29T14:46:00.000Z',
+        now: '2023-01-21T16:48:44.104Z',
+        input: '2022-01-21T16:48:44.104Z',
         expected: '-P1Y',
       },
       {
-        now: '2023-03-23T12:03:00.000Z',
-        input: '2023-03-21T16:03:00.000Z',
-        expected: '-P1DT20H',
+        now: '2023-03-24T20:53:50.104Z',
+        input: '2022-01-21T16:48:44.104Z',
+        expected: '-P1Y2M3DT4H5M6S',
       },
-    ])
-    for (const {input, now, precision = 'millisecond', expected} of elapsed) {
+
+      {
+        now: '2022-01-31T00:00:00.000Z',
+        input: '2022-02-28T00:00:00.000Z',
+        expected: 'P28D',
+      },
+      {
+        now: '2022-02-28T00:00:00.000Z',
+        input: '2022-03-31T00:00:00.000Z',
+        expected: 'P1M3D',
+      },
+      {
+        now: '2022-03-30T00:00:00.000Z',
+        input: '2022-05-01T00:00:00.000Z',
+        expected: 'P1M1D',
+      },
+      {
+        now: '2022-03-31T00:00:00.000Z',
+        input: '2022-05-01T00:00:00.000Z',
+        expected: 'P1M1D',
+      },
+      {
+        now: '2022-04-30T00:00:00.000Z',
+        input: '2022-06-01T00:00:00.000Z',
+        expected: 'P1M2D',
+      },
+      {
+        now: '2024-02-29T00:00:00.000Z',
+        input: '2025-02-28T00:00:00.000Z',
+        expected: 'P11M30D',
+      },
+    ]
+    for (const {input, now, precision = 'millisecond', expected} of elapsedTests) {
       test(`${input} is ${expected} elapsed from ${now} (precision ${precision})`, () => {
         assert.deepEqual(elapsedTime(new Date(input), precision, new Date(now).getTime()), Duration.from(expected))
       })
diff --git a/test/relative-time.js b/test/relative-time.js
index c98a1ae..02e01f6 100644
--- a/test/relative-time.js
+++ b/test/relative-time.js
@@ -452,7 +452,7 @@ suite('relative-time', function () {
       time.setAttribute('tense', 'past')
       time.setAttribute('datetime', '2023-01-01T00:00:00Z')
       await Promise.resolve()
-      assert.equal(time.shadowRoot.textContent, '11 years ago')
+      assert.equal(time.shadowRoot.textContent, '10 years ago')
     })
 
     test('rewrites from now past datetime to minutes ago', async () => {
@@ -1276,25 +1276,25 @@ suite('relative-time', function () {
       {
         datetime: '2022-12-03T15:46:00.000Z',
         format: 'duration',
-        expected: '1 month, 10 days, 1 hour',
+        expected: '1 month, 9 days, 1 hour',
       },
       {
         datetime: '2022-12-03T15:46:00.000Z',
         format: 'duration',
         precision: 'minute',
-        expected: '1 month, 10 days, 1 hour',
+        expected: '1 month, 9 days, 1 hour',
       },
       {
         datetime: '2022-12-03T15:46:00.000Z',
         format: 'duration',
         precision: 'day',
-        expected: '1 month, 10 days',
+        expected: '1 month, 9 days',
       },
       {
         datetime: '2022-12-03T15:46:00.000Z',
         format: 'duration',
         tense: 'future',
-        expected: '1 month, 10 days, 1 hour',
+        expected: '1 month, 9 days, 1 hour',
       },
       {
         datetime: '2022-12-03T15:46:00.000Z',
@@ -1349,25 +1349,25 @@ suite('relative-time', function () {
       {
         datetime: '2024-10-24T14:46:00.000Z',
         format: 'duration',
-        expected: '2 years, 11 days',
+        expected: '2 years',
       },
       {
         datetime: '2024-10-24T14:46:00.000Z',
         format: 'duration',
         precision: 'minute',
-        expected: '2 years, 11 days',
+        expected: '2 years',
       },
       {
         datetime: '2024-10-24T14:46:00.000Z',
         format: 'duration',
         precision: 'day',
-        expected: '2 years, 11 days',
+        expected: '2 years',
       },
       {
         datetime: '2024-10-24T14:46:00.000Z',
         format: 'duration',
         tense: 'future',
-        expected: '2 years, 11 days',
+        expected: '2 years',
       },
       {
         datetime: '2024-10-24T14:46:00.000Z',
@@ -1799,19 +1799,19 @@ suite('relative-time', function () {
       {
         datetime: '2020-10-24T14:46:00.000Z',
         format: 'duration',
-        expected: '2 years, 10 days',
+        expected: '2 years',
       },
       {
         datetime: '2020-10-24T14:46:00.000Z',
         format: 'duration',
         precision: 'minute',
-        expected: '2 years, 10 days',
+        expected: '2 years',
       },
       {
         datetime: '2020-10-24T14:46:00.000Z',
         format: 'duration',
         precision: 'day',
-        expected: '2 years, 10 days',
+        expected: '2 years',
       },
       {
         datetime: '2020-10-24T14:46:00.000Z',
@@ -1823,7 +1823,7 @@ suite('relative-time', function () {
         datetime: '2020-10-24T14:46:00.000Z',
         format: 'duration',
         tense: 'past',
-        expected: '2 years, 10 days',
+        expected: '2 years',
       },
       {
         reference: '2023-03-23T12:03:00.000Z',
@@ -2143,7 +2143,7 @@ suite('relative-time', function () {
       {
         datetime: '2021-10-30T14:46:00.000Z',
         format: 'elapsed',
-        expected: '11m 29d',
+        expected: '11m 24d',
       },
       {
         datetime: '2021-10-30T14:46:00.000Z',
@@ -2152,7 +2152,7 @@ suite('relative-time', function () {
         expected: '11m',
       },
       {
-        datetime: '2021-10-29T14:46:00.000Z',
+        datetime: '2021-10-24T14:46:00.000Z',
         format: 'elapsed',
         expected: '1y',
       },
@@ -2481,7 +2481,7 @@ suite('relative-time', function () {
         datetime: '2022-01-01T12:00:00.000Z',
         tense: 'past',
         format: 'micro',
-        expected: '1y',
+        expected: '11m',
       },
       {
         reference: '2022-12-31T12:00:00.000Z',