How to use this calculator
Use this tool when the rate is already known and you want the new amount. The rate is always applied to the starting value. For negative starting amounts, the multiplier is still correct algebraically, but the words increase and decrease may not describe the numerical direction.
Known rate or unknown rate?
This calculator applies a rate you already know. A salary of 2,400 increased by 5% becomes 2,520: the increase is 120. If you instead know the old and new salaries and need the rate, use the percentage change calculator.
| Known information | Find | Tool |
|---|---|---|
| 2,400 and a 5% increase | New value: 2,520 | This calculator |
| Old value 2,400; new value 2,520 | Rate: 5% | Percentage change |
Why equal increases and decreases do not cancel
Increase 2,400 by 5% to get 2,520. Decrease that result by 5% to get 2,394. The second 5% is taken from the larger base, so the final value is 6 below the original. Multiply the factors: 1.05 × 0.95 = 0.9975, an overall decrease of 0.25%.
For shopping reductions, the discount calculator also reports savings and supports two successive discounts.
The formula
Worked examples
Increase 200 by 10%
200 × 1.10 = 220.
Decrease 200 by 10%
200 × 0.90 = 180.
Increase, then decrease
200 increased by 10% is 220. Decreasing 220 by 10% gives 198, not 200.
Special cases & input limits
A 0% adjustment keeps the value unchanged. A 100% decrease gives zero. Decreases above 100% are permitted here and can make the result negative. Rates must be nonnegative; use the mode to choose direction.
Inputs support a decimal point and scientific notation, up to 30 significant digits and a magnitude of 10⁻²⁰ to 10³⁰, or zero. Select 0–12 display decimal places. Very small or large answers use scientific notation so a nonzero result is not displayed as zero.
A common mistake
Adding 10 rather than multiplying by 1.10 is a fixed amount change, not a 10% increase.
Content updated · Calculation methodology