Percentage increase / decrease calculator
Two tools in one: find the percentage change between two numbers, or apply a percentage rise or fall to any value. The first mode answers “what percent bigger or smaller is this?”; the second answers “what do I get after adding or removing this percent?”. Handy for prices, discounts, pay rises, statistics and everyday maths.
How it works
Pick a mode and the tool applies the matching formula:
% change between values: (new − old) ÷ old × 100
apply a p% change: new = value × (1 + p ÷ 100)In change mode, a positive result is an increase and a negative one a decrease. In apply mode, a negative percentage models a decrease. Results are rounded to six decimals; change is undefined when the old value is 0.
Example
Change mode — from 80 to 100: (100 − 80) ÷ 80 × 100 = +25%, an increase.
Apply mode — a −15% change on 200: 200 × (1 − 0.15) = 170.
| Mode | Inputs | Result |
|---|---|---|
| Change | 80 → 100 | +25% |
| Change | 100 → 80 | −20% |
| Apply | 200, +25% | 250 |
| Apply | 200, −15% | 170 |
Practical uses by mode
When to use “change between values”
This mode is for analysis and reporting: you have a before and an after and want the relative difference. Common uses include year-over-year revenue growth, price changes on a product, changes in test scores, population growth between censuses, and comparing a metric to a benchmark. The output is always a signed percentage — positive for growth, negative for decline.
When to use “apply a percentage”
This mode is for forward-looking calculation: you have a starting point and know what percentage shift to apply. Common uses include:
- Adding a tax or markup to a price (for example, applying a 20% VAT to a net price)
- Calculating a discounted sale price (for example, 30% off a recommended retail price)
- Projecting a salary after a raise
- Modelling a reduction in headcount or budget
Enter a negative percentage to model a decrease — the formula handles both directions with the same value × (1 + p/100) expression.
Chaining multiple changes
Remember that sequential percentage changes do not add linearly. A 10% increase followed by a 10% decrease gives 100 → 110 → 99, a net −1%, because the second percentage applies to the larger intermediate figure. To chain changes, apply each one step at a time using the apply mode, or multiply the factors: for example, +10% then −10% is ×1.10 × 0.90 = ×0.99.
All arithmetic happens locally in your browser, so the numbers you enter never leave your device.