Discount Calculator
Work out a sale price after one discount or several stacked, and see what the discounts actually come to combined.
Result
Enter original price to see the result.
https://calcgallery.com/shopping/discount-calculator/
Results are arithmetic from the amounts and rates you enter. The site publishes no tax rate, threshold or tipping convention, and rates vary by jurisdiction and change. Check the rate on your receipt, invoice or tax authority guidance, and confirm anything that matters with a qualified adviser. Read the full disclaimer
How to use the Discount Calculator
- Choose whether you are working out the sale price or the original price.
- Enter the price you know.
- Add a row for each discount, in the order they are applied.
- Read the effective combined discount, which is the number people get wrong.
How it is calculated
Discounts multiply:
final = original × (1 − d₁) × (1 − d₂) × …effective = 1 − (1 − d₁) × (1 − d₂) × …That is the whole page. What makes it worth having is that almost everyone adds the percentages instead.
What stacked discounts actually come to
| Discounts | Price from 100 | Real discount |
|---|---|---|
| 20% | 80.00 | 20% |
| 20% then 10% | 72.00 | 28%, not 30% |
| 20% then 20% | 64.00 | 36%, not 40% |
| 50% then 50% | 25.00 | 75%, not 100% |
The second discount is taken from a smaller number, so it is worth less in absolute terms than the first. The gap widens as the discounts get larger: two 50% offers leave you paying a quarter, not nothing.
Order does not matter. Multiplication commutes, so 30% then 15% and 15% then 30% give the same price. Shop rules sometimes say which base a coupon applies to, which is a different question; this page applies each discount to what the previous one left.
Working backwards
To find the original price from a sale price, divide by what is left:
original = final ÷ (1 − effective discount)A 72 sale price after 28% off came from 100, because 72 ÷ 0.72 = 100. Adding 28% back to 72 gives 92.16 — the same class of mistake as subtracting a tax rate from a total.
A 100% discount makes this direction undefined: every original price produces a sale price of zero. The page rejects it rather than returning a meaningless number.
Tax
Where a tax rate is entered, it is applied to the discounted price, which is the usual treatment: you are taxed on what you actually pay. A 100 item at 20% then 10% off comes to 72, and 8.25% tax on that is 77.94.
Practical tips
Add the percentages to get an upper bound, never the answer. The real discount is always less.
Two 50% offers are not free. If a shop advertises it that way, the second is applied to the already-halved price.
A single large discount beats two small ones summing to the same number. 40% off beats 20% then 20%.
Check what each coupon applies to. “20% off everything” and “20% off the sale price” are different offers even where the arithmetic looks the same.
With your numbers
- 20% then 10% is 28% off, not 30%: each one applies to what the last one left
- $100.00 less $28.00 saved
- That leaves $72.00
Quick reference
Stacked discounts multiply rather than add. Two 20% discounts are 36% off, not 40%.
| Example | Price after discount |
|---|---|
| 100 at 20% | $80.00 |
| 100 at 20% then 10% | $72.00 |
| 100 at 20% then 20% | $64.00 |
| 100 at 50% then 50% | $25.00 |
| 89.99 at 30% | $62.99 |
| 72 after 28% off | €72.00 |
| 100 at 25% with 8.25% tax | €75.00 |
| 250 at 15% | €212.50 |
Common questions about the Discount Calculator
- Why is 20% then 20% not 40% off?
- Because the second discount applies to what the first one left. Twenty percent off 100 is 80; twenty percent off 80 is 64. You have paid 64, so you saved 36%, not 40%. The shortfall grows with the size of the discounts: two 50% discounts give 75% off, not 100%, which is why stacking two half-price offers never makes anything free.
- Does the order of the discounts matter?
- Not to the result. Multiplication commutes, so 30% then 15% gives exactly the same price as 15% then 30%. Order can matter in a shop if the terms say a coupon applies to the pre-sale price, but that is a rule about which base each discount uses, not about the arithmetic. This page applies each one to what the last one left.
- Is tax worked out before or after the discount?
- After, in most jurisdictions: you are taxed on what you actually pay. This page applies the tax rate to the discounted price for that reason. Where a rule says otherwise, work out the tax separately.
- How do I find the original price from a sale price?
- Divide by what is left after the discount, not multiply by one plus it. A 72 sale price after 28% off is 72 ÷ 0.72 = 100. Adding 28% back to 72 gives 92.16, which is wrong for the same reason subtracting a tax rate from a total is wrong — the percentage was taken from the larger number.
- What happens with a 100% discount?
- Going forwards it is fine: the price becomes zero. Going backwards it is undefined — every original price gives a sale price of zero, so there is nothing to work back to. The page rejects that case rather than dividing by zero and returning something meaningless.