Redeem a Gift Card – Amazon Customer Service

If you want to keep your gift card balance to spend on another occasion, see Keep Your Gift Card Balance to Use Later

If your order total is more than your gift card balance, we’ll charge the remaining
amount to your default payment method.

Often you may use Amazon Gift Cards as a partial form of payment for an item. In
some cases, any new Amazon Gift Card added to your Amazon account will be automatically
applied to the order placed once it’s shipped. For example, if you are adding Amazon
Gift Cards to your Amazon account after the order is placed but not shipped.