In short: Stores stack discounts precisely because the math is unintuitive: 25% off plus another 10% off sounds like 35%, but it is really 32.5%, and the register knows it. This calculator shows the final price, what you actually save, and the true discount percentage.
Updated August 28, 2026, after a fresh review, with updated visuals and links.
It also adds sales tax at the end, because the number that matters is the one that leaves your account, not the one on the yellow sticker.
How stacked discounts really work
Percentage discounts multiply; they do not add. A $100 item at 25% off drops to $75; the extra 10% applies to the $75, taking off $7.50, not $10. Final price: $67.50, a 32.5% effective discount.
Enter price, first discount, an optional second stacked discount, and an optional tax rate. Example: $89.99 with 30% off plus 15% member extra lands at $53.54 before tax; with 8% tax the card gets charged $57.82.
The effective-discount readout is the equalizer: it converts any coupon pile into one honest percentage so you can compare a stack against a single straight discount from a competitor.
Worth remembering
- Compare the final out-the-door price across stores, not the headline percentage; a bigger discount on an inflated base price still loses.
- Clearance math cuts both ways: a $200 item at 70% off still costs $60. Ask if you wanted it before the sale existed.
Frequently asked
Why is 20% + 20% off not 40% off?
Because the second discount applies to the already-reduced price. 100 goes to 80, then 20% of 80 is 16, leaving 64: a 36% total discount. Multiplication, not addition.
Does the order of two stacked discounts matter?
No. 0.75 x 0.90 equals 0.90 x 0.75. What changes the result is mixing percentage-off with fixed-amount coupons; those apply in whatever order the store chooses.
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