Discount Calculator
Enter a price and a discount to get the sale price and the actual saving. A second discount stacks correctly on the reduced price, and tax is applied afterwards the way most retailers charge it.
Formula
- Price
- = the original ticket price
- d₁, d₂
- = the first and any additional discount
- tax
- = sales tax charged on the discounted price
Discounts multiply rather than add, which is why "30% off plus an extra 20% off" is a 44% reduction and not 50%.
How to use this calculator
- Enter the original price shown on the ticket.
- Enter the main discount percentage — 30 for "30% off".
- If the offer stacks ("extra 20% off sale prices"), enter the second discount too. Leave it at 0 otherwise.
- Add a sales tax rate if you want the amount you will actually be charged at the till.
- Press Calculate to see the sale price, the saving and the effective discount across both offers.
Worked example
“30% off, plus an extra 20% off sale prices” on a $250 coat
The two discounts do not add up to 50%. The second applies to the price after the first has already been taken off.
- 250 × 0.70 = 175.00
- 175 × 0.80 = 140.00
- Saving: 250 − 140 = 110.00
Answer: $140.00 — a saving of $110, which is an effective 44% discount, not 50%.
Why stacked discounts disappoint
The intuition that 30% and 20% make 50% is strong and wrong. The second discount is applied to a price that has already shrunk, so it removes 20% of $175 rather than 20% of $250 — $35 instead of $50. The combined effect is a multiplier of 0.70 × 0.80 = 0.56, leaving 56% of the price and saving 44%.
The order of the two discounts does not matter, since multiplication commutes: 0.80 × 0.70 gives the same 0.56. What does matter is whether a stated offer stacks at all. "50% off" and "30% off plus 20% off" are genuinely different promotions, and the difference on a $250 coat is $15.
| Advertised | Multiplier | Effective discount | On $250 |
|---|---|---|---|
| 30% + 20% | 0.70 × 0.80 = 0.560 | 44.0% | $140.00 |
| 50% | 0.50 | 50.0% | $125.00 |
| 25% + 25% | 0.75 × 0.75 = 0.5625 | 43.75% | $140.63 |
| 40% + 10% | 0.60 × 0.90 = 0.540 | 46.0% | $135.00 |
Where tax sits in the sequence
In most jurisdictions that charge tax at the register — including US sales tax — the tax is calculated on the discounted price, because the discount reduces the actual consideration paid. That is the order this calculator uses: discount first, then tax.
In VAT jurisdictions where the shelf price is already tax-inclusive, the arithmetic is different: the discount is applied to a gross price and the tax component shrinks with it automatically. If you need the net-of-tax figure from an inclusive price, use the reverse percentage calculator.
Judging whether a discount is worth it
Two figures matter and only one is advertised. The percentage is what the sign says; the absolute saving is what leaves your account. 40% off a $15 item saves $6. 10% off a $600 item saves $60. The larger percentage is the smaller saving.
The second consideration is the reference price. A discount is only a saving relative to a price you would otherwise have paid, and reference prices are frequently inflated ahead of a sale. Comparing the sale price against what other retailers charge is more reliable than comparing it against the original ticket. The unit price calculator is often more useful than a discount calculation when comparing across pack sizes.
Working the other way
If you know the original and the sale price but not the discount rate, that is a percentage decrease calculation: (250 − 140) ÷ 250 × 100 = 44%. If you know the sale price and the discount rate but need the original, that is a reverse percentage: 140 ÷ 0.56 = $250.
Important considerations
- Discounts stack multiplicatively; two offers never add to their sum.
- Sales tax is normally charged on the discounted price, not the original.
- A percentage discount says nothing about value without the absolute saving and a market reference price.
- Some promotions exclude tax, shipping or specific product lines from the discount base.
- Coupon codes that take a fixed amount off behave differently from percentage codes and should be subtracted after the percentage.
Common mistakes to avoid
- Adding stacked discounts. 30% + 20% is 44% off, not 50%.
- Applying tax before the discount. This overstates the tax and the total.
- Comparing percentages across different prices. The bigger percentage is often the smaller saving.
- Using the sale price as the discount base. That understates the discount you received.
- Assuming the original price was real. Reference prices are frequently set high before a promotion.
Frequently asked questions
How do I calculate a percentage discount?
Multiply the price by (1 − discount ÷ 100). For 30% off $250: 250 × 0.70 = $175. The saving is the difference, $75.
How do stacked discounts work?
The second discount applies to the already-reduced price, so they multiply. 30% then 20% leaves 0.70 × 0.80 = 0.56 of the price — a 44% total reduction, not 50%.
Is tax charged before or after the discount?
After, in almost all sales-tax jurisdictions, because tax is charged on what you actually pay. This calculator applies the discount first and then the tax rate you enter.
How do I work out the discount percentage from two prices?
Subtract the sale price from the original, divide by the original, and multiply by 100. From $250 to $140: 110 ÷ 250 × 100 = 44%.
What is a good discount?
That depends on the absolute saving, not the percentage. 40% off a cheap item can save less than 10% off an expensive one. Compare the final price against what other sellers charge rather than against the original ticket.
Can a discount be more than 100%?
No — a 100% discount already makes the item free, and anything beyond that would mean the retailer pays you. This calculator rejects rates above 100% for that reason.
Related calculators
Tools people usually open alongside this one.
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Reverse Percentage Calculator
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Percentage Calculator
Answer all three percentage questions: X% of Y, X as a percent of Y, and the whole behind a percentage.
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