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diff --git a/date-fns/src/isLeapYear/index.ts b/date-fns/src/isLeapYear/index.ts
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+++ b/date-fns/src/isLeapYear/index.ts
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+import toDate from '../toDate/index'
+import requiredArgs from '../_lib/requiredArgs/index'
+
+/**
+ * @name isLeapYear
+ * @category Year Helpers
+ * @summary Is the given date in the leap year?
+ *
+ * @description
+ * Is the given date in the leap year?
+ *
+ * ### 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 date to check
+ * @returns {Boolean} the date is in the leap year
+ * @throws {TypeError} 1 argument required
+ *
+ * @example
+ * // Is 1 September 2012 in the leap year?
+ * var result = isLeapYear(new Date(2012, 8, 1))
+ * //=> true
+ */
+export default function isLeapYear(dirtyDate: Date | number): boolean {
+  requiredArgs(1, arguments)
+
+  const date = toDate(dirtyDate)
+  const year = date.getFullYear()
+  return year % 400 === 0 || (year % 4 === 0 && year % 100 !== 0)
+}