Why the application order changes the final price
A percentage coupon removes a share of whatever price it's applied to, so applying it to a bigger number removes a bigger amount. Applying the percentage coupon to the full regular price (before the flat coupon shrinks it) always removes more money than applying it after.
- Price — the regular price before either coupon
- % — the percentage coupon
- Flat — the flat-amount coupon
More detail
Proof: the percentage coupon should always go first
Applying % first removes Price×(%÷100) + Flat in total. Applying Flat first removes Flat + (Price−Flat)×(%÷100) — which is Flat×(%÷100) less, because the percentage coupon is now working on a smaller number. That difference, Flat × (%÷100), is the extra amount you lose by using the flat coupon first whenever neither order hits the 0 floor — it's always ≥ 0, so percentage-first never loses. The two orders tie when either coupon is zero, and when both orders bottom out at 0 — a flat coupon that covers the whole price, or a percentage of 100 or more. Near that floor the gap shrinks instead of holding at Flat × (%÷100): with the default coupons on a 6,249 price it is 999.2, not 1,000.
Checkout tip. If a store's checkout applies coupons in a fixed order you can't control, this calculator still tells you whether that order is costing you money — worth knowing before you decide whether it's worth splitting a purchase into two separate transactions to reorder the discounts yourself.
Frequently asked questions
On a 50,000 item with a 20% coupon and a 5,000 flat coupon, which order is cheaper?
Applying the 20% coupon first gives 50,000 × 0.8 − 5,000 = 35,000. Applying the 5,000 flat coupon first gives (50,000 − 5,000) × 0.8 = 36,000. The percentage-first order is 1,000 cheaper.
Does the better order ever change depending on the numbers?
No — applying the percentage coupon first is mathematically at least as good in every case, and strictly better whenever both are greater than zero and the result doesn't hit the 0 floor. The size of the saving changes with the numbers, but which order wins does not.
What if the flat coupon is bigger than the discounted price?
The final price is floored at 0 in both orders rather than going negative, so if the flat coupon alone exceeds the price, both application orders can end in a tie at 0 — enter your numbers above to check.
Can I control which coupon a store applies first?
Usually not at checkout, since most carts apply both automatically in a fixed order. If the difference matters and the store allows separate transactions or manual coupon entry, applying the percentage coupon to the largest possible base first is the one that saves more.