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diff --git a/date-fns/src/getDayOfYear/index.ts b/date-fns/src/getDayOfYear/index.ts
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+++ b/date-fns/src/getDayOfYear/index.ts
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+import toDate from '../toDate/index'
+import startOfYear from '../startOfYear/index'
+import differenceInCalendarDays from '../differenceInCalendarDays/index'
+import requiredArgs from '../_lib/requiredArgs/index'
+
+/**
+ * @name getDayOfYear
+ * @category Day Helpers
+ * @summary Get the day of the year of the given date.
+ *
+ * @description
+ * Get the day of the year of the given date.
+ *
+ * ### 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} date - the given date
+ * @returns {Number} the day of year
+ * @throws {TypeError} 1 argument required
+ *
+ * @example
+ * // Which day of the year is 2 July 2014?
+ * const result = getDayOfYear(new Date(2014, 6, 2))
+ * //=> 183
+ */
+export default function getDayOfYear(dirtyDate: Date | number): number {
+  requiredArgs(1, arguments)
+
+  const date = toDate(dirtyDate)
+  const diff = differenceInCalendarDays(date, startOfYear(date))
+  const dayOfYear = diff + 1
+  return dayOfYear
+}