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Coupon Stacking Calculator

Which order to apply a percentage and a flat coupon. Percentage first is always at least as good, because applying the flat amount first shrinks the base the percentage works on.

Also called: stack coupons, coupon order.

$
%
$
Apply first
$
Best achievable price
$81.00

$81.00 by applying the percentage coupon first. Percentage first gives $81.00 and flat first gives $84.00, a difference of $3.00.

Percentage first
$81.00
Flat amount first
$84.00
Difference between the two orders
$3.00
Which to apply first
percentage
Total saved
$39.00
How this is calculated
Method and background

How this is calculated

A flat coupon applied before a percentage reduces the amount the percentage can discount, so you lose the percentage of the flat coupon. Percentage first preserves the full base, then the flat amount comes off in full. The difference is exactly the percentage times the flat coupon, which on a large flat voucher is not trivial. Checkouts vary in which order they apply, and some let you choose.

applying a flat amount before a percentage discounts the flat amount too
V
Cart total (currency)
d
Percentage coupon (decimal)
F
Flat coupon (currency)

Worked examples

Each of these is asserted on every build. If a change to the engine ever moved one of these answers, the build would fail before the page could print it.

twenty percent off and fifteen dollars off

Cart total
$120.00
Percentage coupon
20%
Flat amount coupon
$15.00
Apply first
Percentage
Shipping
$0.00

Best achievable price$81.00

Percentage first: 120 x 0.8 = 96, less 15, is 81. Flat first: 105 x 0.8 = 84. The 3 difference is exactly 20% of the 15 voucher, which is the general result and the reason order matters.

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no flat coupon makes order irrelevant

Cart total
$120.00
Percentage coupon
20%
Flat amount coupon
$0.00
Apply first
Percentage
Shipping
$0.00

Best achievable price$96.00

boundary: with nothing for the percentage to be applied before or after, both orders give 120 x 0.8 = 96

Open this example

no coupons is the cart total

Cart total
$120.00
Percentage coupon
0%
Flat amount coupon
$0.00
Apply first
Percentage
Shipping
$0.00

Best achievable price$120.00

degenerate case: nothing applied leaves the cart exactly as it was

Open this example

Method and limits

What it assumes

  • Both coupons are stackable, which many are not.

What it deliberately does not model

  • Minimum spend thresholds may be evaluated before or after other discounts.

Formula version 1.0.0 · definition 1.0.0 · United States · Report a problem with this calculator

Frequently asked questions

Which order should I want?
Percentage first, always. Applying a flat voucher first means the percentage discount has a smaller base, so you lose the percentage of the voucher.