18% Off: Calculate the Sale Price, Original Price and Extra Discount

Quick answer with a stated starting price

18% off means removing 18 parts out of every 100 of the original price. For an example price of 680 units, the saving is 680 × 18/100 = 122.4. The amount remaining is 680 − 122.4 = 557.6.

The remaining fraction is 82%, or 0.82. You can calculate the sale price directly as original price × 0.82. 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, 1360, the same discount saves 244.8 and leaves 1115.2. 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: 122.4 + 557.6 = 680. To check the rate itself, divide the saving by the original price and multiply by 100: 122.4 ÷ 680 × 100 = 18%.

Recover the original price

If all you know is that the sale price is 557.6 after 18% off, divide by the remaining fraction: 557.6 ÷ 0.82 = 680. Do not add 18% of the sale price: that percentage would use a smaller base.

For this example, adding 18% to the reduced price would give 657.968, which does not restore 680. 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 557.6, then multiply by 0.90 for a further 10% off. The final amount is 501.84 before any currency rounding. The overall discount is 26.2%, not 28%.

The second saving is 10% of 557.6, equal to 55.76. It is smaller than 10% of the original 680. Reading “extra” as a sequence of multiplications explains the difference without a special rule.

Rounding and a practical check

Keep the unrounded multiplier 0.82 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.