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diff --git a/date-fns/src/differenceInCalendarWeeks/index.ts b/date-fns/src/differenceInCalendarWeeks/index.ts
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+import startOfWeek from '../startOfWeek/index'
+import getTimezoneOffsetInMilliseconds from '../_lib/getTimezoneOffsetInMilliseconds/index'
+import requiredArgs from '../_lib/requiredArgs/index'
+import { LocaleOptions, WeekStartOptions } from '../types'
+
+const MILLISECONDS_IN_WEEK = 604800000
+
+/**
+ * @name differenceInCalendarWeeks
+ * @category Week Helpers
+ * @summary Get the number of calendar weeks between the given dates.
+ *
+ * @description
+ * Get the number of calendar weeks between the given dates.
+ *
+ * ### v2.0.0 breaking changes:
+ *
+ * - [Changes that are common for the whole library](https://github.com/date-fns/date-fns/blob/master/docs/upgradeGuide.md#Common-Changes).
+ *
+ * @param {Date|Number} dateLeft - the later date
+ * @param {Date|Number} dateRight - the earlier date
+ * @param {Object} [options] - an object with options.
+ * @param {Locale} [options.locale=defaultLocale] - the locale object. See [Locale]{@link https://date-fns.org/docs/Locale}
+ * @param {0|1|2|3|4|5|6} [options.weekStartsOn=0] - the index of the first day of the week (0 - Sunday)
+ * @returns {Number} the number of calendar weeks
+ * @throws {TypeError} 2 arguments required
+ * @throws {RangeError} `options.weekStartsOn` must be between 0 and 6
+ *
+ * @example
+ * // How many calendar weeks are between 5 July 2014 and 20 July 2014?
+ * const result = differenceInCalendarWeeks(
+ *   new Date(2014, 6, 20),
+ *   new Date(2014, 6, 5)
+ * )
+ * //=> 3
+ *
+ * @example
+ * // If the week starts on Monday,
+ * // how many calendar weeks are between 5 July 2014 and 20 July 2014?
+ * const result = differenceInCalendarWeeks(
+ *   new Date(2014, 6, 20),
+ *   new Date(2014, 6, 5),
+ *   { weekStartsOn: 1 }
+ * )
+ * //=> 2
+ */
+export default function differenceInCalendarWeeks(
+  dirtyDateLeft: Date | number,
+  dirtyDateRight: Date | number,
+  dirtyOptions?: LocaleOptions & WeekStartOptions
+): number {
+  requiredArgs(2, arguments)
+
+  const startOfWeekLeft = startOfWeek(dirtyDateLeft, dirtyOptions)
+  const startOfWeekRight = startOfWeek(dirtyDateRight, dirtyOptions)
+
+  const timestampLeft =
+    startOfWeekLeft.getTime() - getTimezoneOffsetInMilliseconds(startOfWeekLeft)
+  const timestampRight =
+    startOfWeekRight.getTime() -
+    getTimezoneOffsetInMilliseconds(startOfWeekRight)
+
+  // Round the number of days to the nearest integer
+  // because the number of milliseconds in a week is not constant
+  // (e.g. it's different in the week of the daylight saving time clock shift)
+  return Math.round((timestampLeft - timestampRight) / MILLISECONDS_IN_WEEK)
+}