diff --git a/src/plugin/duration/index.js b/src/plugin/duration/index.js
index e2060c344..2e7bcdd05 100644
--- a/src/plugin/duration/index.js
+++ b/src/plugin/duration/index.js
@@ -127,13 +127,8 @@ class Duration {
   toISOString() {
     const Y = getNumberUnitFormat(this.$d.years, 'Y')
     const M = getNumberUnitFormat(this.$d.months, 'M')
-
-    let days = +this.$d.days || 0
-    if (this.$d.weeks) {
-      days += this.$d.weeks * 7
-    }
-
-    const D = getNumberUnitFormat(days, 'D')
+    const W = getNumberUnitFormat(this.$d.weeks, 'W')
+    const D = getNumberUnitFormat(this.$d.days, 'D')
     const H = getNumberUnitFormat(this.$d.hours, 'H')
     const m = getNumberUnitFormat(this.$d.minutes, 'M')
 
@@ -148,6 +143,7 @@ class Duration {
     const negativeMode =
       Y.negative ||
       M.negative ||
+      W.negative ||
       D.negative ||
       H.negative ||
       m.negative ||
@@ -156,7 +152,7 @@ class Duration {
     const T = H.format || m.format || S.format ? 'T' : ''
     const P = negativeMode ? '-' : ''
 
-    const result = `${P}P${Y.format}${M.format}${D.format}${T}${H.format}${m.format}${S.format}`
+    const result = `${P}P${Y.format}${M.format}${W.format}${D.format}${T}${H.format}${m.format}${S.format}`
     return result === 'P' || result === '-P' ? 'P0D' : result
   }
 
@@ -261,6 +257,7 @@ class Duration {
 const manipulateDuration = (date, duration, k) =>
   date.add(duration.years() * k, 'y')
     .add(duration.months() * k, 'M')
+    .add((duration.$d.weeks || 0) * k, 'w')
     .add(duration.days() * k, 'd')
     .add(duration.hours() * k, 'h')
     .add(duration.minutes() * k, 'm')
diff --git a/test/plugin/duration.test.js b/test/plugin/duration.test.js
index 3e726af91..773914b21 100644
--- a/test/plugin/duration.test.js
+++ b/test/plugin/duration.test.js
@@ -55,7 +55,18 @@ describe('Creating', () => {
       weeks: 5,
       months: 6,
       years: 7
-    }).toISOString()).toBe('P7Y6M39DT3H2M1.1S')
+    }).toISOString()).toBe('P7Y6M5W4DT3H2M1.1S')
+  })
+  it('object with only weeks', () => {
+    expect(dayjs.duration({
+      weeks: 2
+    }).toISOString()).toBe('P2W')
+  })
+  it('object with year and weeks', () => {
+    expect(dayjs.duration({
+      year: 1,
+      week: 2
+    }).toISOString()).toBe('P1Y2W')
   })
   it('object with millisecond', () => {
     expect(dayjs.duration({
@@ -100,14 +111,29 @@ describe('Parse ISO string', () => {
   })
   it('ISO string with week', () => {
     const d = dayjs.duration('P2M3W4D')
-    expect(d.toISOString()).toBe('P2M25D')
+    expect(d.toISOString()).toBe('P2M3W4D')
     expect(d.asDays()).toBe(85.83333333333333) // moment 86, count 2M as 61 days
     expect(d.asWeeks()).toBe(12.261904761904763) // moment 12.285714285714286
     expect(d.asMonths()).toBe(2.8219178082191783) // moment 2.8213721020965523
   })
+  it('ISO string with only weeks', () => {
+    expect(dayjs.duration('P3W').toISOString()).toBe('P3W')
+  })
+  it('ISO string preserves weeks and days separately', () => {
+    expect(dayjs.duration('P2Y3W5D').toISOString()).toBe('P2Y3W5D')
+  })
+  it('ISO string with weeks and time components', () => {
+    expect(dayjs.duration('P1Y2W3DT4H5M6S').toISOString()).toBe('P1Y2W3DT4H5M6S')
+  })
   it('Invalid ISO string', () => {
     expect(dayjs.duration('Invalid').toISOString()).toBe('P0D')
   })
+  it('Negative duration with weeks', () => {
+    expect(dayjs.duration({
+      weeks: -2,
+      days: -3
+    }).toISOString()).toBe('-P2W3D')
+  })
 })
 
 it('Is duration', () => {
@@ -209,6 +235,15 @@ test('Add duration', () => {
   const b = dayjs('2023-02-01 00:00:00')
   const p = dayjs.duration('P1Y1M1DT1H1M1S')
   expect(b.add(p).format('YYYY-MM-DD HH:mm:ss')).toBe('2024-03-02 01:01:01')
+
+  // Test duration with weeks
+  const c = dayjs('2020-01-01')
+  const weeks = dayjs.duration({ week: 2 })
+  expect(c.add(weeks).format('YYYY-MM-DD')).toBe('2020-01-15')
+
+  const d = dayjs('2020-01-01')
+  const weeksAndDays = dayjs.duration('P2W3D')
+  expect(d.add(weeksAndDays).format('YYYY-MM-DD')).toBe('2020-01-18')
 })
 
 describe('Subtract', () => {
@@ -225,6 +260,15 @@ test('Subtract duration', () => {
   const b = dayjs('2023-03-02 02:02:02')
   const p = dayjs.duration('P1Y1M1DT1H1M1S')
   expect(b.subtract(p).format('YYYY-MM-DD HH:mm:ss')).toBe('2022-02-01 01:01:01')
+
+  // Test duration with weeks
+  const c = dayjs('2020-01-20')
+  const weeks = dayjs.duration({ week: 2 })
+  expect(c.subtract(weeks).format('YYYY-MM-DD')).toBe('2020-01-06')
+
+  const d = dayjs('2020-01-20')
+  const weeksAndDays = dayjs.duration('P1W5D')
+  expect(d.subtract(weeksAndDays).format('YYYY-MM-DD')).toBe('2020-01-08')
 })
 
 describe('Seconds', () => {