Discount calculator
20% off a price of 100 gives a sale price of 80. An extra 10% off that reduced price brings it to 72, a combined saving of 28%, not 30%.
What this calculator does
Use this discount calculator to turn a percentage-off offer into a sale price and a cash saving. Enter the original price and the first discount. If another offer applies to the reduced price, enter it in the optional extra discount field. Leave that field empty for a single offer; an empty extra discount counts as zero.
The result shows the sale price, total saving and effective combined discount. Each percentage is applied in sequence to the amount left by the previous offer. This is useful for sale prices, extra promotional codes and comparisons between a single large offer and two smaller offers. It does not decide whether a retailer allows coupons to be combined or which items qualify for an advertised promotion.
Formula
Sale price = original price × (1 − first discount ÷ 100)
Or in one step: With an extra discount: original × (1 − first ÷ 100) × (1 − extra ÷ 100)
In plain English, work out the fraction of the price still payable after each offer and multiply those fractions by the original price. Total saving is the original price less the final sale price. The effective discount is one minus the product of the remaining fractions, multiplied by 100. Prices must be zero or more, and each discount must be from 0% to 100%.
Worked example
An original price of 100 has 20% off, followed by another 10% off. The first offer leaves 100 × 0.8 = 80. The second leaves 80 × 0.9 = 72. The total saving is 28, so the effective combined discount is 28% of the original price.
Worked example: a sale price with 25% off
A bag has an original price of 80 and a 25% sale offer. The remaining fraction is 1 − 25 ÷ 100 = 0.75. Multiply 80 by 0.75 to get a sale price of 60. The cash saving is 80 − 60 = 20. In this example, one quarter of the original price is saved.
Use the original price that actually forms the base of the offer. A manufacturer's suggested price, a previous selling price and the current ticket price may not be the same amount. The calculator compares the figures you enter; it does not verify a claimed reference price or establish whether an advertised saving is fair.
Worked example: two half-price offers
An item originally costs 200 and receives 50% off followed by another 50% off the sale price. The first offer leaves 100. The second leaves 50, so the saving is 150. As a share of the original price, 150 out of 200 is 75%, not 100%. Each offer halves what is left rather than removing half the original price twice.
For a quick comparison with another promotion, use the effective combined percentage rather than adding the advertised rates. On the same original price, a single 80% offer would leave 40 and would be larger than these two 50% offers. That comparison assumes both promotions apply to the same item without additional conditions.
Sale-price formulas in Excel and Google Sheets
Put the original price in A1, the first discount as an ordinary number in B1 and the extra discount in C1. Use =A1*(1-B1/100)*(1-C1/100) for the sale price. An empty C1 is treated as zero in this arithmetic. Total saving is A1 minus the sale-price cell.
For the effective discount as an ordinary number, use =(1-(1-B1/100)*(1-C1/100))*100. If B1 and C1 instead contain percentage-formatted values such as 20% and 10%, omit their divisions by 100. Keep the original and final prices numeric, use currency formatting for display, and validate each rate before relying on the comparison.
Everyday examples
| Example | Answer | Try it |
|---|---|---|
| Single offer: 20% off 100 | 80 | |
| Stacked offer: 20% then 10% off 100 | 72 | |
| Two half-price offers on 200 | 50 | |
| Sale code: 20% then 10% off £39.99 | £28.79 |
Common mistakes
- Adding stacked rates together. Two offers of 20% and 10% leave 72% of the original price, so the combined saving is 28%, not 30%.
- Calculating the extra saving from the original price. A sequential coupon applies to the reduced price unless the offer explicitly says otherwise.
- Confusing the amount saved with the amount paid. Check the Sale price and Total saving labels rather than using whichever number looks familiar.
- Ignoring fixed fees, minimum spends and exclusions. Delivery charges or a coupon cap may change the final bill even when the percentage arithmetic is correct.
Common questions
How do I calculate 20% off a price?
Multiply the original price by 0.8, because 80% remains payable after 20% off. A price of 100 becomes 80, with a saving of 20. Enter the price and 20 as the discount, leaving the optional extra discount empty.
Are 20% off and an extra 10% off the same as 30% off?
No. The second offer applies to the reduced price. Starting from 100, 20% off leaves 80 and another 10% off leaves 72. The total saving is 28%, while a single 30% offer would leave a price of 70.
What is the effective combined discount?
It is the single percentage-off rate that would produce the same final price. For two sequential offers, multiply their remaining fractions and take that product away from one. For 20% and 10%, the calculation is (1 − 0.8 × 0.9) × 100 = 28%.
Does the order of two percentage discounts matter?
Not in this pure multiplication model: 0.8 × 0.9 equals 0.9 × 0.8. Fixed-price coupons, rounding after each stage, eligibility rules and maximum savings can make real checkout results order-dependent. Follow the offer terms rather than assuming every promotion behaves like two unrestricted percentages.
Can I leave the extra discount blank?
Yes. A blank extra discount is treated as 0%, so it does not change the first sale price. You can also enter zero explicitly. A malformed extra value is not ignored: the calculator asks for a valid number so a typing error does not silently change the result.
What happens at 100% off?
The price becomes zero and the total saving equals the original price. Any further percentage offer still leaves zero payable. Rates below zero or above 100% are rejected because this tool models ordinary percentage-off offers, not surcharges or payments to the buyer.
Why can the checkout differ by a penny?
This calculator keeps decimal precision between stages and rounds the displayed money result at the end. A retailer may round each line or each discount separately. Check their rounding rules and any delivery charges, taxes or coupon restrictions when comparing the result with a receipt.
Last reviewed . Results use exact decimal arithmetic and are rounded once for display.
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