Discount Calculator

Checked 15 October 2026. What was checked. How these pages are maintained.

Sale price math

Sale price = original × (1 − discount%). Amount saved = original − sale. Original = sale ÷ (1 − discount%). A $80 item at 25% off is $60. You save $20.

Worked example

A $80 jacket at 25% off is $60. You save $20. If the tag already shows $60 at 25% off, the original was $80.

Two discounts in a row usually multiply: 20% then 10% on $80 is $57.60, which is 28% off, not 30%. Ontario HST on the $60 sale price is $7.80, so the till shows $67.80. Add tax on the sale price, not on the original, unless the store taxes first (rare on retail receipts).

One tag, then a second tag

This form applies one percent off. A $120 jacket at 15 percent off is 120 × 0.85 = $102. You save $18. A second sign that says 10 percent off the sale price is not another field here. Take the $102 and run it again: 102 × 0.90 = $91.80. The combined saving is $28.20, which is 28.20 ÷ 120 = 23.5 percent off the original, not 25 percent. Twenty and ten do not add to thirty when the second cut is on a smaller price. The Everyday Fig video on the $80 jacket is the same rule with a 25 percent tag.

To reverse a tag, switch the form to original price. A $91.80 sale at 10 percent off came from 91.80 ÷ 0.90 = $102. Reverse the 15 percent the same way: 102 ÷ 0.85 = $120. Dividing by the percent that remains is the whole trick. Subtracting 15 percent from the sale price goes the wrong direction.

Tax sits on the sale price

This page stops before the till. In Ontario, 13 percent HST on the $102 sale is $13.26, so the receipt is $115.26 if only the first discount applied. Tax on the original $120 would be wrong unless the store actually does that, which ordinary retail receipts do not. Use the GST/HST calculator on the sale price, not on the crossed-out price. A coupon for a fixed dollar amount is not a percent. Subtract the dollars first, then run any percent that still applies, in the order the receipt uses.

Watch the same example

The video walks through the $80 jacket in the example: one discount, tax at the till, two discounts in a row, and reversing a sale tag.

Common questions