Percentage Decrease Calculator
Enter the original and the new, lower value and see how many percent it dropped. You can also take a percentage off a price here.
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The formula
Percentage decrease = ((Old value - New value) / Old value) x 100
How to work out a percentage decrease
Subtract the new value from the old one, divide by the old value, then multiply by 100. The result is how much of the original has gone.
This calculator uses one shared engine with the percentage change tool, so if you type a higher second number it will tell you the value increased rather than give a negative answer.
A worked example
A phone drops from 800 to 680. The drop is 120. 120 / 800 = 0.15, so the price fell by 15%.
To reduce a number by a percentage instead, pick "Decrease X by Y%". Taking 20% off 55 gives 55 x 0.80 = 44.
Why a fall and a rise are not symmetrical
If something loses 50% of its value and then gains 50%, it does not return to the start. 100 falls to 50, then rises 50% to 75. To get back to 100 from 50 you need a 100% rise. This is why large losses in investing are so hard to recover from.
Examples to check
Type these into the calculator above to see how it behaves. Every result below was produced by the same calculator code that runs on this page.
| What you enter | What you get |
|---|---|
| Percentage change from X to Y; Starting value (X): 800; New value (Y): 680 | Percentage decrease: 15% |
| Percentage change from X to Y; Starting value (X): 250; New value (Y): 200 | Percentage decrease: 20% |
| Percentage change from X to Y; Starting value (X): 60; New value (Y): 45 | Percentage decrease: 25% |
| Percentage change from X to Y; Starting value (X): 100; New value (Y): 120 | Percentage increase: 20% |
Percentage Decrease Calculator: frequently asked questions
How do I take a percentage off a price?
Multiply the price by 1 minus the percentage as a decimal. For 30% off, multiply by 0.70.
Can a percentage decrease be more than 100%?
Not for something that cannot go below zero, like a price or a headcount. A fall of 100% means it hit zero. Values that can go negative, such as a bank balance, can drop by more than 100%.
How do I turn a percentage into a decimal?
Divide by 100, or move the decimal point two places to the left. So 15% is 0.15, 5% is 0.05 and 120% is 1.2. Multiplying by that decimal is exactly how every percentage calculation works.
Can a percentage be more than 100?
Yes. 150% of a number is one and a half times that number. Percentages above 100 show up all the time with growth: if sales went from 40 to 100, they grew by 150%.
Why does a 50% rise followed by a 50% fall not bring me back to where I started?
Because the second percentage is taken from a bigger number. Start at 100, rise 50% to 150, then fall 50% and you land on 75. The same trap catches people with investments and sale prices.
How accurate is this calculator?
It uses standard double-precision arithmetic, accurate to about 15 significant digits. Results are rounded only for display.
Last reviewed: October 3, 2026