20% Off: Calculate the Sale Price, Original Price and Extra Discount

Quick answer with a stated starting price

20% off means removing 20 parts out of every 100 of the original price. For an example price of 720 units, the saving is 720 × 20/100 = 144. The amount remaining is 720 − 144 = 576.

The remaining fraction is 80%, or 0.8. You can calculate the sale price directly as original price × 0.8. The example uses arbitrary currency units and excludes taxes, delivery and other charges.

A second price to check the method

At twice the original price, 1440, the same discount saves 288 and leaves 1152. The rate is unchanged even though the cash saving doubles. A fixed amount off would behave differently.

Check the first calculation by adding the saving and sale price: 144 + 576 = 720. To check the rate itself, divide the saving by the original price and multiply by 100: 144 ÷ 720 × 100 = 20%.

Recover the original price

If all you know is that the sale price is 576 after 20% off, divide by the remaining fraction: 576 ÷ 0.8 = 720. Do not add 20% of the sale price: that percentage would use a smaller base.

For this example, adding 20% to the reduced price would give 691.2, which does not restore 720. Subtracting and adding the same percentage cancel only when both percentages are calculated from the same base.

An extra 10% off is applied sequentially

Apply the first discount to reach 576, then multiply by 0.90 for a further 10% off. The final amount is 518.4 before any currency rounding. The overall discount is 28%, not 30%.

The second saving is 10% of 576, equal to 57.6. It is smaller than 10% of the original 720. Reading “extra” as a sequence of multiplications explains the difference without a special rule.

Rounding and a practical check

Keep the unrounded multiplier 0.8 until the final step. A shop may round individual items or the order total, so tiny differences can appear when many prices are combined. Use the receipt’s actual rounding policy when checking a purchase.

Compare the final total for the same quantity and delivery terms. A larger discount percentage does not necessarily mean a lower price when the starting prices differ. This guide explains arithmetic, not an offer from any particular seller.

Check the mathematical definitions

For fractions, percentages and worked arithmetic, see OpenStax Prealgebra. For number definitions, see OpenStax on prime and composite numbers and Wolfram MathWorld on digital roots. Worked examples on this page are calculated for this guide.