Prime Day offers offers over a million discounts and deals, but you can stack discount codes to save even more

• Amazon Prime Day is happening now, and runs until July 16 at 11:59 p.m. PT.
• Prime Day 2019 offers discounts on over a million items - but by "stacking" discounts, you can save even more money.
• For instance, you can stack promo codes that get $5 off certain orders to get multiple $5 discounts at once.
• Plus, if you have an American Express card that earns Membership Rewards points, link it to your Amazon account to see if you're targeted for 20% off your order by July 16. If you're targeted, you only need to use one Amex point to get this discount.
• See all of our favorite Amazon Prime deals and discounts »

Amazon Prime Day is all about discounts, but beyond the million-plus slashed prices, there are some valuable Amazon discount codes going around - including some that can be stacked to get you savings on multiple orders.

$5 off at least $25 in gift cards with code GCPRIME19

If you purchase at least $25 in Amazon gift cards, entering the promo code GCPRIME19 will get you a $5 promo credit. According to the offer page, the $5 credit will be applied to your account within two days of your digital gift card purchase, or within two days of your physical gift card purchase shipping.

$5 off a $50-plus order with the code SHIP2ME

While the $5 promo code from your qualifying Amazon gift card purchase may not hit your account until Prime Day is over, if you purchased a digital gift card, you can use it immediately toward another Amazon purchase.

So, stack the gift card with another deal: Using the promo code SHIP2ME will get you $5 off a purchase of $50 or more on a Prime-fulfilled item. So that's $5 off the purchase made (at least in part) with your gift card, plus $5 off a future Amazon order.

$5 off print book purchases with the code PRIMEBOOK19

Yet another potentially stackable deal is $5 off physical book purchases of $15 or more with the code PRIMEBOOK19. You could use your $25 gift card in tandem with this $5 off for books.

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Stack Prime Day discounts with 20% off when you use even just one Amex point

If you have an American Express card that earns Amex Membership Rewards points, check to see if you're targeted for 20% off an Amazon purchase when you use Amex points to cover at least a portion of your order. You'll need to link one of your Membership Rewards-earning cards to your Amazon account.

If you have an eligible Amex card and you're targeted, you can get 20% off an Amazon purchase, with a maximum discount of $50 (so 20% off up to a $250 purchase). This 20% discount expires at 11:59 p.m. PT, the same time that Prime Day concludes.Note that this offer hasn't been working with the PRIMEBOOK19 code mentioned above.

Up to 25% off Amazon devices when you use just one Amex point

Similar to the structure of the offer mentioned above, if you're targeted for this Amex Membership Rewards deal on Amazon, you can get discounts of up to 25% off Amazon-brand electronics, including 25% off the Fire TV Stick and 20% off the all-new Kindle.

You need to use Amex points to cover at least a portion of your order, and you need to click to activate the specific offer you're interested in to get the discount.

Don't pay for your entire order with points

While you could pay for your entire Amazon order with Amex points, your points are only worth 0.7 cents apiece when redeemed through Amazon. That might not mean much on its own, but travel website The Points Guy lists Amex Membership Rewards points at a value of 2 cents each. That valuation is thanks to the fact that you can transfer Amex points to airline and hotel partners and book first-class flights and hotel award stays that could cost you hundreds or thousands of dollars out of pocket.

That's all to say that you should only pay the minimum of one point required to get the 20% discount. Make sure you changed the number of points applied to your order to "one" and select the Amex card that's the source of your Amex points on Amazon as the payment method for the remainder of the order.

The Amazon Prime credit card always earns 5% back on Amazon and Whole Foods purchases - but on Prime Day, it's 6% »