How to decrease a number by a percentage
The quickest method is the multiplier: subtract the percentage from 100, turn it into a decimal, and multiply once.
Decreasing 250 by 15% becomes 250 × 0.85 = 212.5. One multiplication, no separate subtraction step, and it works for any percentage. The multiplier is simply the proportion left behind: take 15% off and 85% remains, take 30% off and 70% remains. Thinking of it that way keeps the arithmetic honest when discounts start stacking up, because you multiply the multipliers rather than adding the percentages.
Type your starting number and the percentage above and the calculator applies the multiplier for you, showing the new value and exactly how much came off. It handles decimals, large numbers and percentages over 100 without complaint.
Worked examples
The mistake to avoid: reversing a decrease
Undoing a percentage decrease is not the same as adding the percentage back on. If a jacket costs £90 in a 25% off sale, the original price is 90 ÷ 0.75 = £120. Adding 25% to £90 gives £112.50, which is wrong, because the 25% was calculated on the larger original price, not the sale price. Always divide by the multiplier to go backwards.
This trips people up constantly with discounts, pay cuts and value drops. If you only know the before and after figures and want the percentage between them, that is a different question: our percentage change calculator answers it directly.
A related mix-up is percentages versus percentage points. If a savings rate falls from 40% to 30%, it has dropped by 10 percentage points but decreased by 25%, because 10 is a quarter of 40. News reports switch between the two without warning, so when a headline says a figure "fell by 10%", it is worth pausing to check which one is meant. The gap between the two readings can be enormous.
Repeated decreases do not add up
Two 10% cuts are not a 20% cut. Start with 200: the first cut takes you to 180, the second takes 10% of 180 and lands on 162, an overall fall of 19%. Multipliers multiply, so 0.9 × 0.9 = 0.81, meaning 81% remains. The same logic explains why a 50% drop followed by a 50% rise leaves you worse off: 100 falls to 50, then rises to 75, because 0.5 × 1.5 = 0.75.
Retailers lean on this in "extra discount" promotions. An extra 20% off stock already reduced by 30% is 0.70 × 0.80 = 0.56 of the original price, a 44% total discount rather than the 50% your instinct suggests. Run each step through the calculator, or multiply the multipliers, and the true saving falls straight out.
Frequently asked questions
How do I decrease a number by a percentage?
Subtract the percentage from 100, turn it into a decimal and multiply once. To decrease 250 by 15%, multiply 250 × 0.85 = 212.5. The multiplier method is quicker and less error-prone than working out the percentage separately and subtracting it.
How do I work out a sale price?
Multiply the full price by 1 minus the discount as a decimal. 20% off a £64.99 jacket is 64.99 × 0.80 = £51.99, a saving of £13.00. For 30% off, multiply by 0.70 instead.
How do I reverse a percentage decrease?
Divide by the multiplier rather than adding the percentage back. If a price is £90 after a 25% reduction, the original was 90 ÷ 0.75 = £120. Adding 25% to £90 would give £112.50, which is wrong.
Can I decrease a number by more than 100%?
You can, but the result goes negative. Decreasing 40 by 150% gives 40 × (1 − 1.5) = −20. For prices and quantities, a decrease of 100% (down to zero) is the practical limit.
What is the difference between percentage decrease and percentage change?
A percentage decrease applies a known percentage to a starting number to get a new, smaller value. Percentage change works the other way round: you know both values and want the percentage between them. Use our percentage change calculator for that.