🏷 Discount Calculator (Percent Off)
Five shopping discount calculations on one page. Change any number and the answer updates instantly.
How to use it
Each box is its own calculator — change the two numbers in the one you need and its answer updates underneath. The result panel on the right sums up all five, and the copy button grabs the whole summary for a note or a message.
Discount formulas
| What you want | Formula | Example |
|---|---|---|
| Percent off | (original − sale) ÷ original × 100 | $80 → $56 = 30% off |
| Sale price | original × (1 − % off ÷ 100) | 25% off $129.99 = $97.49 |
| Stacked discount | 1 − (1 − A) × (1 − B) | 20% + 10% = 28% |
| Original price | sale ÷ (1 − % off ÷ 100) | $35.91 at 30% off = $51.30 |
| Buy N get M free | M ÷ (N + M) × 100 | Buy 2 get 1 = 33.3% off |
Shopping math that trips people up
20% off plus an extra 10% off is not 30% off
The second discount applies to the already reduced price: $100 → 20% off = $80 → extra 10% off = $72. That is 1 − 0.8 × 0.9 = 0.28, a 28% total discount. The order does not matter (10% first then 20% also gives $72). Only a coupon that explicitly says both apply to the original price gets you 30%.
BOGO is 50% off — only if you use both
Buy one get one free means two items for the price of one: 50% off each. Buy 2 get 1 free is 3 for the price of 2, about 33.3% off each. Those percentages only matter if you actually need the extra items; otherwise BOGO is just spending more.
Working backward to the original price
If something is "$35.91 after 30% off", the original is 35.91 ÷ 0.7 = $51.30, not 35.91 × 1.3 ($46.68). Adding the percentage back always undershoots — use box ④.
Percent off vs. dollars saved
10% off a $1,200 laptop saves more than 50% off a $30 shirt. And "up to 70% off" usually applies to a handful of items. Cash back and store credit come after checkout and may have strings attached, so they are not the same as a lower price.
Compare unit prices on bulk items
For multipacks and family sizes, the unit price (per ounce, per count) is more reliable than any "sale" tag. An 18 oz box for $4.99 is 27.7¢/oz; a 30 oz box for $7.49 is 25¢/oz — about 10% cheaper. Most US grocery shelf tags show the unit price in small print.
Remember sales tax
US shelf prices usually exclude sales tax, which is added at the register. Apply the discount first, then tax: a $56 sale price in a 7% tax area costs $59.92.
Results are rounded to the cent. Actual checkout prices can differ because of store rounding rules, coupon caps, minimum purchase conditions and sales tax.