B·02 · Groceries and deals
Discount and percent off calculator
This discount calculator gives you the price you pay after one or more percent-off discounts, and works back to the original price when all you know is the sale price.
The bar is the full price: the yellow part is what you pay, the hatched pieces are what each discount takes off. Each discount is worked out on the price already reduced, so the percentages don't add up.
What to buy
Your measurements
You pay 35.93 instead of 49.90: you save 13.97, a total discount of 28%
To buy
- 1Item at 35.93 instead of 49.90
Estimate only: always go by what the product label says.
Link copied
Estimate only: always go by what the product label says.
How to work out a discount
The sale price is the full price times (100 - discount) ÷ 100: 20% off 49.90 leaves 49.90 × 0.8 = 39.92, so the discount is worth 9.98. When there is more than one discount, the second one comes off the price already reduced by the first, and a third comes off the result of the second. That is why the factors multiply: 20% and then 10% off is 0.8 × 0.9 = 0.72, so you pay 72% of the full price. The total discount is 28%, not 30%.
To go the other way, divide: original price = sale price ÷ (100 - discount) × 100. The calculator does both. Pick "Sale price" at the top to start from the price tag. There is no currency, and cents are rounded only in the result.
A worked example: 49.90 with 20% off, then 10% off
These are the values the calculator opens with.
| Step | Worked out on | Takes off | Left to pay |
|---|---|---|---|
| 20% off | 49.90 | 9.98 | 39.92 |
| 10% off | 39.92 | 3.99 | 35.93 |
You pay 35.93 and save 13.97, a total discount of 28%. The second discount takes off 3.99, not 4.99, because the 10% is worked out on 39.92. Adding the percentages would give 30% off and a price of 34.93, almost 1 less than the real one.
With "Sale price" the calculator opens on an item at 34.93 after 30% off: the original price was 34.93 ÷ 0.7 = 49.90, and you save 14.97.
Stacked discounts: what they are really worth
| Discounts | Total discount | Added up (wrong) |
|---|---|---|
| 10% + 10% | 19% | 20% |
| 20% + 10% | 28% | 30% |
| 20% + 20% | 36% | 40% |
| 30% + 10% | 37% | 40% |
| 30% + 20% | 44% | 50% |
| 40% + 10% | 46% | 50% |
| 50% + 10% | 55% | 60% |
| 50% + 20% | 60% | 70% |
| 50% + 50% | 75% | 100% |
| 70% + 20% | 76% | 90% |
| 20% + 10% + 5% | 31.6% | 35% |
| 30% + 20% + 10% | 49.6% | 60% |
The order of the discounts doesn't change the final price: 10% and then 20% off 49.90 still ends at 35.93. Only the amount each one takes off changes, 4.99 for the first and 8.98 for the second.
Store deals: extra % off, buy 2 get 1 free, second item half price
An "extra 10% off" at checkout on clearance items is a second, stacked discount: 30% off and then an extra 10% off an 80.00 item brings it to 56.00 and then 50.40, 37% off in total. In the calculator that is two discount rows.
Deals on several items turn into a percentage per item. Buy 2 get 1 free (3 for 2 in UK shops) means you pay for 2 items out of 3, 33.3% off each; buy 3 get 1 free is 25% off. Second item half price, on two identical items, is 25% off, not 50%. To compare a 3 for 2 with a 30% discount, enter 33.33 as the discount and 3 as the items. It is the better deal, as long as you actually need all three.
Common mistakes
- Adding the discounts up. 20% plus 10% off is 28%, not 30%: the second discount is worked out on a lower price.
- Going back to the original price by adding the percentage. 34.93 plus 30% is 45.41, not 49.90. The 30% was worked out on the full price, so you have to divide by 0.7.
- Taking the second discount off the full price. 10% off after 20% off 49.90 is 3.99, not 4.99.
- Rounding at every step. If you round to the cent after each discount, the result can be a cent off the exact figure. The calculator keeps every digit and rounds only at the end.
Last reviewed: October 8, 2026 · About us
35.93