It's the same as in store. 21 days with tags attacthed, for instore credit or exchange.

No refunds on anything- store credit for more defective and bad goods, and pitiful customer services.
Better places to spend your hard earned money WITH a full refund.

This is cut and pasted from their Web site:
RETURNS & EXCHANGES

All store purchases may only be returned to stores within the original country of purchase. Please contact your local store for return policy information.

Online purchases made through forever21.com may be returned within 30 days of the ship date. Your return form and invoice provide a postmark date that specifies the last day you have to return your merchandise by mail or to our stores. Refunds will be made in the form of the original payment and are only available for online purchases returned by mail. Merchandise returned to any Forever 21, XXI Forever, or ForLove21 location within the United States will be eligible for exchange or store credit towards your next purchase. Final sale items cannot be returned or exchanged.

Items must be returned unworn (sanitary liner intact for swimwear), unwashed, and unused, with tags attached and must be accompanied by the original return form and customs documents (if applicable).

Gift cards, e-gift certificates, cosmetics, jewelry, and final sale merchandise may not be returned for a refund, credit, or exchange; unless received damaged, defective, or the wrong item(s) was shipped.

For online you have 30 dayd to return to store for exchange or store credit. I think you can try getting your money back only way is you return it back but of course you pay shipping and you'll get a check.