Percentage Decrease Calculator
Choose whether you want to take a percentage off a number or find the percentage drop between two values, fill in the fields and press Calculate. The guide below shows the formula and several worked cases.
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Created by the Reeliy Editorial Team. Last updated: Oct 19, 2026
How to calculate percentage decrease
A percentage decrease says how much a quantity has shrunk, measured against where it started. Because the starting value is the yardstick, it always goes in the denominator.
percentage decrease = (original − new) ÷ original × 100
- Subtract the new value from the original value to get the size of the drop.
- Divide that drop by the original value.
- Multiply by 100 to express it as a percentage.
If the new value turns out to be larger than the original, the formula gives a negative number. The calculator shows it with a minus sign, which simply means the quantity went up rather than down; for that situation the percentage increase calculator is the more natural tool.
Decreasing a number by a given percentage
When you already know the percentage and want the reduced value, work with a multiplier instead.
new value = original × (1 − percentage ÷ 100)
amount removed = original × percentage ÷ 100
Reducing 250 by 18% gives 250 × 0.82 = 205, and the amount removed is 250 × 0.18 = 45. For shop prices and coupons, the percent off calculator and the discount calculator apply the same arithmetic.
Using the calculator
- Decrease by %: enter the original value and the percentage. You get the decreased value and the absolute difference, which is the amount taken off.
- Percentage decrease (x to y): enter the original value and the new value. You get the percentage decrease and the absolute difference between the two values.
Results are rounded to two decimals. A whole number is shown without decimals (170, not 170.00), anything else with exactly two (12.50%), and large numbers are grouped with commas. Negative numbers cannot be entered, and in the second mode the original value cannot be zero because the percentage would be undefined.
Worked examples
All of the figures below can be reproduced in the calculator.
A price that dropped
A pair of headphones went from 84 to 63. The drop is 84 − 63 = 21, and 21 ÷ 84 = 0.25, so the price fell by 25%.
Lower household spending
Monthly grocery spending went from 640 to 568. The saving is 72, and 72 ÷ 640 = 0.1125, which is a decrease of 11.25%.
Pay after a deduction
A gross monthly pay of 4,800 is reduced by a 22% deduction. The amount withheld is 4,800 × 0.22 = 1,056, leaving 4,800 × 0.78 = 3,744. Use the real rate from your own payslip, since actual deductions vary by country and by band.
Change in body weight
Someone who weighed 92 kg and now weighs 85.1 kg has lost 6.9 kg. Then 6.9 ÷ 92 = 0.075, a decrease of 7.5%, which the calculator displays as 7.50%.
Why a decrease and its reverse are not equal
A percentage is always taken from the current base, so undoing a drop needs a larger percentage on the smaller base. Falling from 100 to 80 is a 20% decrease, but climbing back from 80 to 100 takes a 25% increase.
increase needed to recover = decrease ÷ (100 − decrease) × 100
| Decrease | Increase needed to get back |
|---|---|
| 10% | 11.11% |
| 20% | 25% |
| 30% | 42.86% |
| 40% | 66.67% |
| 50% | 100% |
| 75% | 300% |
Percentage changes do not simply add or cancel. A 10% fall followed by a 10% rise leaves you at 99% of the start, because 0.90 × 1.10 = 0.99.
Common mistakes
- Dividing by the new value instead of the original one, which understates the drop.
- Mixing up percent and percentage points: a rate that falls from 8% to 6% dropped by 2 points, which is a 25% decrease.
- Treating a decrease of more than 100% as possible for quantities that cannot go below zero. A price cannot lose 130% of its value; if the formula says so, the inputs are probably the wrong way round.
- Averaging several percentage drops. Multiply the individual factors (0.9 × 0.8 × …) instead.
For a general-purpose tool that also answers "what is X% of Y?" questions, see the percentage calculator.
Frequently asked questions
How do you calculate percentage decrease?
Subtract the new value from the original, divide the result by the original and multiply by 100. For example, going from 200 to 170 is a drop of 30, and 30 ÷ 200 × 100 = 15%.
How do I reduce a number by a percentage?
Multiply the number by 1 minus the percentage written as a decimal. To take 15% off 200, calculate 200 × 0.85 = 170.
Why does the calculator show a negative percentage decrease?
A negative result means the new value is higher than the original, so the quantity increased. Going from 150 to 200 shows -33.33% because the value rose by a third of its starting level.
Can I calculate a percentage decrease from zero?
No. The original value is the denominator of the formula and dividing by zero is undefined, so the calculator reports an error. In that case only the absolute change is meaningful.
Cite this calculator and page
If you use this page in your work, you can cite it as:
Reeliy Editorial Team. (2026). Percentage Decrease Calculator. Reeliy. https://reeliy.com/calculators/percent-decrease-calculator“Percentage Decrease Calculator.” Reeliy, 2026, https://reeliy.com/calculators/percent-decrease-calculator.