How to Calculate a Discount and Sale Price
3 min read · Last reviewed July 1, 2026
Sale signs are designed to look generous, and working out what you'll actually pay keeps you in control. The maths behind '30% off' is quick once you've seen it, and you can often do it in your head at the shelf.
This guide covers the discount formula, a mental shortcut, how to handle two discounts stacked together, and where sales tax fits in.
The discount formula
The saving is the original price multiplied by the discount percentage divided by 100. For 30% off a 80 item: 80 × 0.30 = 24 off, giving a sale price of 80 − 24 = 56.
A faster route to the final price is to multiply by what you'll still pay: 30% off means you pay 70%, so 80 × 0.70 = 56 in a single step.
A mental-maths shortcut
Find 10% by moving the decimal one place left, then build the discount from it. For 30% off 45: 10% is 4.50, so 30% is 13.50, making the sale price 31.50.
For odd percentages, round to estimate. 15% off is 10% plus half of 10% again — quick enough to sanity-check a till total before you pay.
Stacked discounts and tax
Two discounts don't simply add up. An extra 20% off an item already reduced by 30% isn't 50% off — the second cut applies to the already-lower price. 80 becomes 56 after 30%, then 56 × 0.80 = 44.80, an effective 44% off, not 50%.
Sales tax, where it applies, is added after the discount, on the reduced price. So the order is: take the discounts first, then apply tax to whatever's left.
Frequently asked questions
▶How do I calculate the final price after a discount?
Multiply the original price by the percentage you'll still pay. For 25% off, you pay 75%, so a 60 item costs 60 × 0.75 = 45.
▶Do two stacked discounts add together?
No. The second discount applies to the already-reduced price, so 30% off then 20% off is about 44% off in total, not 50%. Apply them one after the other.
Try the calculators
Work out the sale price and how much you save from a percentage discount.
Open calculator →Add sales tax or VAT to a price to see the tax amount and total you'll pay.
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