Percentage Decrease Calculator

Percentage decrease formula

To reduce a number by a percentage, work out that percentage of the number and subtract it. Or, in one step, multiply by one minus the percentage as a decimal:

amount of decrease = original × (percentage ÷ 100)
new value = original × (1 − percentage ÷ 100)

So a 25% decrease is "× 0.75", a 10% decrease is "× 0.9" and a 100% decrease always gives zero.

Worked examples

Example 1: 25% off a $120 jacket

Discount: 120 × 0.25 = 30. Sale price: 120 − 30 = 90. Or directly: 120 × 0.75 = 90.

Example 2: a car worth 28,000 losing 15% in a year

Depreciation: 28,000 × 0.15 = 4,200. New value: 23,800.

Example 3: cutting a 45-minute commute by 12%

Reduction: 45 × 0.12 = 5.4 minutes. New commute: 39.6 minutes, about 39 minutes 36 seconds.

How to read the result

The big number is the value after the decrease, with the amount removed shown underneath. The amber bar shows how much of the original remains: after a 25% decrease, three quarters of the bar is filled. The formula line repeats the calculation with your inputs so you can check it.

If you enter a decrease above 100%, nothing of the original is left: the remaining share reads "0% (past zero)" and a note explains how far below zero the value has gone. That can be legitimate — for example, a profit falling by 150% becomes a loss — but for prices and physical quantities it usually signals a typo.

Stacked discounts

Retailers sometimes offer "an extra 20% off sale prices". Discounts like this multiply rather than add. A 30% discount followed by an extra 20% is 0.7 × 0.8 = 0.56 of the original price, a total discount of 44% — not 50%. To compute a stacked discount with this tool, run it once for the first discount, then use the result as the new original number for the second.

The order of percentage discounts does not matter (0.8 × 0.7 is the same as 0.7 × 0.8), but mixing a percentage discount with a fixed-amount coupon does: taking $10 off before 20% gives a different total than after.

Limits of the formula

The formula takes the percentage of the original number. It is not the right tool for reversing an increase: if a price including 20% tax is 120, the pre-tax price is 120 ÷ 1.2 = 100, not 120 minus 20% (96). Use division by the growth factor for that.

Negative percentages are rejected because a negative decrease is an increase — use the percentage increase calculator for that. If you have the before and after values and want to know the percentage, the percentage change calculator is the right choice. Real-world depreciation is usually applied year by year on a declining balance, so a 15% annual rate over three years is 0.85³ ≈ 0.614, a total decline of about 38.6%, not 45%.

Also remember that percentage decreases are relative to a base that changes over time. A shop that cuts prices by 10% every week does not reach zero after ten weeks; it reaches 0.9¹⁰ ≈ 35% of the original price. Repeated percentage decreases shrink a value toward zero but never quite reach it, which is why half-life and depreciation schedules behave the way they do. For a one-off cut, though, the simple formula above is exact, and the result shown is the precise value before any rounding you apply for currency or measurement.

Common uses

Shoppers use percentage decreases to check sale prices and compare deals across stores. Businesses use them to plan cost cuts, model churn and apply volume discounts. Accountants apply declining-balance depreciation to equipment and vehicles, and fitness or nutrition plans often express targets as a percentage reduction, such as cutting sugar intake by 20%. Engineers and scientists use them for tolerances and losses — for example, a battery that keeps 80% of its capacity has lost 20%.

Knowing both the new value and the amount removed matters: the first tells you what you will pay or have left, the second tells you how much you saved or lost.

Common mistakes

A common trap is assuming a discount can be reversed by adding the same percentage back. If a $200 item is reduced by 20% to $160, adding 20% to $160 gives $192, not $200 — the reverse step needs a 25% increase. Another is comparing "percent off" offers with different bases, such as 30% off one item versus 15% off an entire basket. Convert each offer to an amount saved with this calculator before deciding which is better.