Discount Calculator

Percentages off are designed to be read quickly and checked slowly. "40% off, plus an extra 20% at the till" sounds like 60% but is not; a shelf ticket may measure its saving against a price nobody paid; and a sale price alone tells you nothing until you know what it was reduced from. This calculator does the two pieces of arithmetic that settle those questions — the sale price and saving from an original price and a percentage, and the original price implied by a sale price and a claimed discount.

The two calculations

The top card runs the discount forward. The saving is the original price multiplied by the discount percentage, and the final price is the original minus that saving. With the defaults — $100 at 25% — you save $25.00 and pay $75.00, which is what the three result cards show alongside the crossed-out original.

The reverse card works backwards. Given a sale price and the discount applied, the original was sale price ÷ (1 − discount ÷ 100). A $75 item at 25% off came from $100, because $75 is 75% of the original and you are undoing that multiplication. This is why you divide rather than adding the percentage back: adding 25% to $75 gives $93.75, not $100 — a trap worth remembering whenever you reverse a percentage.

One behaviour to know: editing anything in the top card copies its result down into the reverse card, so the two stay in sync. To check an unrelated price, type directly into the reverse fields and leave the top card alone. At 100% the reverse result shows a dash, because a free item has no recoverable original.

Stacked discounts are not added

This is the most useful thing to understand about sale pricing. Successive discounts multiply, they do not add:

• 20% off, then a further 10% off the reduced price, leaves 80% of 90% — 72% of the original, so a 28% total discount, not 30%.
• 50% off, then an extra 20%, leaves 40% of the original: a 60% discount, not 70%.
• Three cuts of 30%, 20% and 10% leave 50.4% of the original — a 49.6% discount, not the 60% the labels imply.

To handle this here, run the first discount, copy the final price into the Original Price field, and apply the next percentage. The order of two percentage discounts never changes the answer, because multiplication is order-independent — but order matters enormously when one stage is a fixed amount. "$10 off, then 20% off" and "20% off, then $10 off" give different totals on the same item, and stores are rarely accidental about which sequence they use.

Reading the offer, not the label

• "90% off" means you pay 10%, not 90%. The quick buttons set 10, 25, 30, 50, 75 and 90 percent off, so the 90% button leaves a tenth of the price.
• Buy one, get one half price is a 25% discount across the two items, not 50% — you pay for 1½ items and take home 2.
• Buy two, get one free is a third off across three items, about 33.3%, which you can confirm by entering the three-item total.
• "Up to 70% off" describes the single best-reduced item in the range, so price the specific thing you want.
• Reference prices vary. A discount may be measured against a recommended retail price rather than what the store charged last week, and the reverse card is a quick way to spot an implausible "original".
• Percentage points are not percentages. Moving from a 30% to a 40% discount is 10 percentage points more off, but the amount you hand over falls by only about 14%.

What the tool leaves out

Both cards work in pre-tax money. In most US states sales tax is charged on the discounted price, so the saving is real but the amount at the register is higher than the final price shown here — run the result through the sales tax calculator. Shipping, restocking fees and coupon minimums sit outside the calculation too. There is also no field for entering two prices to get the percentage between them; for that, use the percentage calculator. Splitting a discounted bill? The split bill calculator takes it from there.

How to use the Discount Calculator

1. Enter the original price in the first field.
2. Type the discount percentage, or press a quick button for 10, 25, 30, 50, 75 or 90 percent off.
3. Read the result panel: the crossed-out original, the new price in large type, and the three cards for original price, amount saved and final price.
4. For stacked offers, copy the final price back into the Original Price field and apply the next percentage.
5. To work backwards, use the reverse card: enter the sale price you have been quoted and the discount claimed, and read the implied original.
6. Remember that touching the top card overwrites the reverse card's fields, so do reverse checks separately.

Frequently Asked Questions

Is 20% off plus another 10% the same as 30% off?

No. The second discount applies to the already-reduced price, so you pay 72% of the original — a 28% discount. Stacked percentages always come out lower than their sum.

How do I calculate two or more discounts here?

Apply the first, put the resulting final price into the Original Price field, and apply the second. Repeat for each stage. Order does not affect the answer for percentage discounts, but it does when one stage is a fixed dollar amount.

How do I find the original price from a sale price?

Use the reverse card. Enter the sale price and the discount applied, and it divides by (1 − the discount) to recover the original. A $60 item at 40% off started at $100.

Why do the reverse fields change when I edit the top card?

By design — the forward result is pushed down so both views agree. To check an unrelated price, type into the reverse fields and do not touch the ones above.

Does the final price include sales tax?

No, everything shown is pre-tax. In most places tax is applied to the discounted price, so calculate the discount first and add tax to that figure.

Can it tell me what percentage discount I got?

Not as a direct input, but the arithmetic is simple: divide the amount saved by the original price and multiply by 100. A $30 saving on a $120 item is 25% off.

If a price is cut 25% and later raised 25%, is it back to normal?

No. A $100 item reduced by 25% is $75; raising that by 25% gives $93.75. Increases and decreases are calculated on different bases, which is exactly why the reverse card divides instead of adding.