How to use it
- Type the Price before discounts.
- Type one discount on each line in Discounts, one per line, in order, as name; value. Use % for a percentage.
- Type the Coupon if you have one, and choose whether it is applied before or after the discounts.
- Read the Final price and the Single equivalent discount, then compare them with the wrong way in the table.
How discounts one after another are calculated
A percentage takes its share of the price left by the discount before it, not of the original price. A discount of 20% and then 10% leaves 80% × 90% = 72% of the price: a single discount of 28%. Each discount is rounded to the cent when it is taken, as a till does.
Wikipedia's article on trade discounts describes several discounts combined as a series, for example 20/12/5 for three separate functions. The article gives no formula for them, so the rule here is the plain arithmetic of applying each percentage to the price left.
Price after a percentage = price before × (1 − percentage ÷ 100)
Price after an amount = price before − amount (not below zero)
Single equivalent discount = (price − final price) ÷ price × 100Why adding the percentages is wrong
Adding 20% and 10% gives 30%, which would take 30% of the price. The 10% is taken from the price left after the 20%, which is smaller, so it takes less than 10% of the original price. On 200, 20% and then 10% gives 144, not the 140 that adding the percentages gives.
The more discounts there are, the bigger the gap. Three discounts of 20% each add up to 60%, but one after another they leave 0.8 × 0.8 × 0.8 = 51.2% of the price, a single discount of 48.8%.
Coupon before or after the discounts
With percentages alone, the order does not change the final price. With amounts it does: 50 off 200 and then 20% gives 120, while 20% and then 50 off gives 110. The coupon's terms say where it is applied; the calculator follows the position you choose.
What this calculator does not include
- Tax, such as VAT, which some shops add before the discounts and some after.
- Shipping fees and minimum-spend rules that cancel a coupon.
- Discounts that apply to only some items in a basket. Work out each item's price separately.
Worked example: 200 with three discounts and a 10% coupon
Each discount takes its share of the price left: 20% of 200 is 40, leaving 160; 10% of 160 is 16, leaving 144; 5% of 144 is 7.20, leaving 136.80; the 10% coupon takes 13.68, leaving 123.12.
The single equivalent discount is (200 − 123.12) ÷ 200 = 38.44%. Adding the percentages gives 20 + 10 + 5 + 10 = 45%, a price of 110.00, which is 13.12 less than the price the shop charges. That difference is the mistake.
| Step | Price after |
|---|---|
| Seasonal sale, 20% | 160.00 |
| Member discount, 10% | 144.00 |
| Clearance, 5% | 136.80 |
| Coupon, 10% | 123.12 |
Frequently asked questions
Is 20% and then 10% the same as 30% off?
No. The 10% is taken from the price left after the 20%, so the two together give 28% off. Adding them to 30% overstates the discount, and the price looks lower than the shop will charge.
Does the order of percentage discounts change the price?
No. Percentages multiply, so 20% and then 10% gives the same price as 10% and then 20%. The order matters only when an amount is mixed with percentages.
What happens when a coupon is larger than the price left?
The amount taken is limited to the price left, so the price stops at zero. The calculator shows a note when this happens.
Why is the single equivalent discount useful?
It puts several offers on one scale. Two shops with different chains of discounts can be compared by their final prices, or by the one percentage that gives the same price.
Is the price or the list of discounts sent to a server?
No. The calculation runs in your browser, and nothing you enter is sent to us.
Sources
Figures and text last checked on Tuesday, November 10, 2026.