Percentage Decrease Calculator
Take a percentage off any number and see the new value and exactly how much was removed.
Percentage Decrease Calculator calculates in your browser.
Take a percentage off a number
Use this when you know where a value starts and the percentage it should shrink by — a budget line cut by 12%, energy use reduced by a quarter, a stock count trimmed by 7.5%. You get the new value and the amount removed together. A decrease of exactly 100% brings any value to 0, and larger decreases are allowed but flagged, because they take the value below zero.
How to use the Percentage Decrease Calculator
- Type the starting value.
- Type the percentage to take off.
- Read the new value and the decrease amount, with the working underneath. Copy Result copies a line such as “200 decreased by 15% = 170 (a decrease of 30)”.
The formula
decrease = starting value × percentage ÷ 100
new value = starting value − decrease
shortcut: new value = starting value × (1 − percentage ÷ 100)
A decrease is always a share of the starting value, which is why decreases and increases don’t cancel out: 100 up 20% is 120, and 120 down 20% is 96, because the second 20% is taken of 120. Once the percentage passes 100, the multiplier (1 − percentage ÷ 100) turns negative — 200 × (1 − 1.25) = −50 — so the result drops below zero.
| Decrease | Amount removed | New value |
|---|---|---|
| 200 − 15% | 30 | 170 |
| 80 − 12.5% | 10 | 70 |
| 0.3 − 10% | 0.03 | 0.27 |
| 200 − 100% | 200 | 0 |
| 200 − 125% | 250 | -50 |
Calculated on your device
- The calculation runs in your browser as you type; nothing is sent to a server.
- The values, percentages, and results are not sent to Looty Tools or stored.
- Refreshing the page clears the boxes.
Limitations
- The starting value and the percentage must both be 0 or more. To add a percentage instead, use the Percentage Increase Calculator.
- Decreases over 100% are calculated as written and give a negative result. Whether that makes sense depends on what you are measuring; a price or a count usually can’t go below zero.
- Results are not rounded to cents. For prices, the Discount Calculator rounds to the cent and labels the sale price and savings.
- Values can be up to 1,000,000,000,000,000 with up to 10 decimal places; use a period for decimals.
Related calculators
- Percentage CalculatorFind a percentage of a number.
- Percentage Change CalculatorMeasure the percent change between two numbers.
- Discount CalculatorFind the sale price after a percent off.
Guides
- Decrease by a PercentageTake a percentage off a number in two steps or with one multiplier, see how repeated cuts combine, and learn to reverse a decrease correctly.
- Why Decreases Don’t Undo IncreasesWhy going up 25% and then down 25% leaves you lower than you started, how big the gap gets, and the percentage that really reverses a change.
- Percentage Decrease ExamplesWorked percentage decreases for budgets, prices, and time, what a 100% decrease means, and when a decrease of more than 100% is real or a mistake.
Percentage Decrease Calculator FAQ
- How do you decrease a number by a percentage?
- Work out that percentage of the number and subtract it: 15% of 200 is 30, so 200 becomes 170. In one step, multiply by 1 minus the percentage divided by 100: 200 × 0.85 = 170.
- What does a 100% decrease do?
- It takes the whole value away, so the result is exactly 0.
- Can a decrease be more than 100%?
- Mathematically, yes, and the calculator allows it: a 125% decrease on 200 removes 250 and leaves −50. A note appears when this happens, because many real quantities — a price, a weight, a headcount — can’t go below zero.
- Does a 20% decrease undo a 20% increase?
- No. 100 increased by 20% is 120, but 120 decreased by 20% is 96, because the decrease is taken of the larger number. To get back from 120 to 100 you need a decrease of about 16.67%.
- How is this different from the Discount Calculator?
- The arithmetic is the same. The Discount Calculator is set up for prices: it shows money to the cent, labels the results as sale price and savings, and doesn’t allow discounts over 100%.
- Why can’t I enter a negative value or percentage?
- This calculator takes a percentage off a value of 0 or more. A negative percentage would really be an increase, so the box points you to the Percentage Increase Calculator instead.
- Are the numbers I enter sent anywhere?
- No. The calculation runs in your browser as you type. The numbers you enter and the results are not sent to Looty Tools or stored; refreshing the page clears them.
