Stacked Discount Calculator
Apply percent-off steps and fixed coupons in order and see what each deducts, the true final price, the single equivalent discount, and how far off the naive sum would be.
Also available as a desktop app for Windows.
About this tool
The most expensive mistake in discount shopping is adding percentages. 20% off followed by another 10% off feels like 30% off, but the second discount applies to what the first one left behind: 100 becomes 80, and 10% of 80 is 8, not 10. The real combined discount is 28%, and on a 20% + 10% + 5% stack the gap is worth 3.40 on every 100 — 68.40 actual against a 65.00 gut feeling.
Fixed-amount coupons break the other assumption, that order never matters. With percent-only stacks it truly does not — multiplication commutes, 20% then 10% is the same as 10% then 20%. But the moment a coupon enters, sequence changes the answer: on 100, taking 10 off first and then applying 20% off leaves 72, while 20% off first followed by 10 off leaves 70. That is why the step table above settles each step in your order and shows the running price, so you can match the checkout’s math line for line.
The equivalent-single-discount figure is the honest summary of the whole stack: one percentage that does the same damage. And the work-backwards box answers the question people actually walk into a sale with — not “what does this cost” but “what is the most expensive thing my budget can cover once these discounts are applied”.
Frequently asked questions
- Why isn’t 20% + 10% the same as 30% off?
- Because the second discount is taken from a smaller base. 20% off 100 leaves 80; the extra 10% comes off 80, which is 8 — total 28 off, not 30. Stores often advertise such stacks as “extra 10% on top of 20% off”, which is accurate but easy to mishear as a flat 30%. The gap grows with each step and with the price.
- Does the order of discounts matter?
- Not when every step is a percentage — multiplication is commutative, so any order gives the same final price. Order matters as soon as a fixed-amount coupon is involved: applying the coupon first lets the percentage act on a smaller remainder, which is better for you. On 100 with 20% off and 10 off, coupon-first leaves 70 and percent-first leaves 72.
- What is an “equivalent single discount”?
- One percentage that, applied alone to the original price, gives the same final price as the whole stack. A 20% + 10% stack is equivalent to a flat 28% off. It is the right number for comparing one store’s complicated promotion against another store’s simple one.
- What if a coupon is bigger than the price?
- The fixed step is capped at what remains — the price never goes below zero. In real shops a coupon like that simply zeroes out the bill (and rarely, the remainder). If you are using the work-backwards box and get “no solution”, a coupon is likely eating the entire price somewhere in the middle, which breaks the straightforward arithmetic.
- Does this include tax, shipping or loyalty points?
- No — it models exactly the steps you enter, in the order you enter them. If tax is added after discounts in your jurisdiction, add the discounted total and the tax rate separately. Loyalty points and store credit behave like a fixed step at the very end if you want to model them.
- Does anything I enter get sent anywhere?
- No. Every calculation is plain arithmetic in the page. There is no server, no request and no logging, and the tool keeps working with the network switched off.