Discount calculator
Compare unit price and savings after consecutive discounts, with a quantity total.
Fill in the fields and the result will appear here automatically.
A promotion should be compared by the amount paid, not by adding the percentages printed on its signs. Apply a first discount as a percentage or fixed amount, then an optional percentage discount to the reduced price. The main result and savings refer to one item. Quantity adds a total for identical items receiving the same reductions. This helps compare a fixed coupon with a percentage offer or check an extra ten percent promotion. The form does not recover an original price, accept a second fixed coupon or add tax and delivery to the entered price.
How it works
Formula and logic
For original unit price P, a first percentage d gives F1 = P × (1 − d / 100). A first fixed discount s gives F1 = P − min(s, P). A second percentage e gives F = F1 × (1 − e / 100). Unit savings S = P − F; the effective percentage is S / P × 100%; quantity cost is F × q. The displayed savings remain per item. Percentage discounts are bounded to 0–100 with a visible warning when adjusted; the normal form also validates this range. An amount above the price makes the price zero with a warning, while a negative amount is an error. Active numeric fields must be finite; unknown modes and fractional quantities are rejected. Arithmetic retains precision until display. Monetary amounts of at least one unit display as whole units; smaller nonzero amounts retain decimal precision. This is an estimate, not a reproduction of a retailer’s checkout rounding.
Example
At a price of 1000, a first discount of 20% leaves 800 and a second 10% leaves 720. Unit savings are 280 and the combined discount is 28%, not 30%. Three items cost 2160; displayed unit savings stay 280. With a fixed first discount of 250 followed by 10%, the calculation is 750 × 0.9 = 675, savings 325, effective discount 32.5% and three-item total 2025. Boundary cases: a price of 500 with 0% discount stays 500. A fixed discount of 1000 on that price is bounded to 500, producing zero with a warning. A negative fixed discount or quantity of 1.5 produces an error.
Fields and units
- Original price — $
- Mode — By percent / By amount
- Discount, % — unitless
- Discount amount — monetary units
- Additional discount, % — unitless
- Quantity — unitless
How to use
- — Enter a positive original price per item, using the monetary unit displayed by the form.
- — Choose a percentage or fixed amount for the first discount. Only the visible first-discount field is used.
- — Enter an optional second percentage discount. It applies after the first reduction, rather than adding to its percentage.
- — Use a positive whole-number quantity. Compare unit price and savings with the separate purchase total; tax and delivery are not added.
Method and limitations
- Calculation method
- Formula and logic
- Limitation
- Estimate using the supplied price and discount order with display rounding. Tax, shipping, coupon conditions and retailer checkout rounding are not calculated automatically.
FAQ
Why do 20% off and an extra 10% off produce a 28% discount?
The second ten percent applies to the remaining eighty percent of the original price. The factor is 0.8 × 0.9 = 0.72, leaving savings of 28%. Two discounts of 20% produce 0.8 × 0.8 = 0.64, or a combined reduction of 36%.
Can a fixed coupon be followed by a percentage discount?
Yes. Choose an amount for the first discount and enter the second percentage separately. A price of 1000 minus 250, then minus 10%, becomes 675. The form cannot reverse that order or apply a second fixed amount; check that its order matches the promotion.
Which discount result covers the whole item quantity?
Only the item total multiplies the final unit price by quantity. The main price, savings and original price remain per item. To find total savings, multiply unit savings by quantity yourself: 280 for each of three items gives 840. The displayed savings row does not perform this multiplication.
How are excessive discounts and invalid quantities handled?
A fixed discount above the price is limited to the price, so the final amount cannot be negative. A negative fixed amount is rejected. Percentages outside 0–100 are bounded with a warning, while the form reports a range error. Quantity must be a whole number of at least one and is not silently rounded.
Does the discounted price include tax, shipping and coupon restrictions?
The entered price is used as supplied. Tax is neither separated nor added; shipping, fees, minimum-order requirements and coupon exclusions are not calculated. Price and fixed discount must use the same monetary unit shown in the form and result. Changing the page language does not exchange money.