How is percentage increase or decrease calculated?

Percentage change = (new value − old value) ÷ old value × 100. A positive result is an increase, a negative result is a decrease. Applying a p% change to a value V gives V × (1 + p/100).

How accurate are the results?

Calculations use standard IEEE-754 double-precision arithmetic and are rounded to six decimal places for display. They are exact for everyday financial and statistical use; percentage change is undefined when the original value is 0.

How do I apply a percentage increase to a number?

Multiply by 1 plus the percentage as a decimal. A 20% increase on 250 is 250 × 1.20 = 300. In "apply" mode, just enter 250 and 20.

How do I apply a percentage decrease?

Enter a negative percentage in "apply" mode, or multiply by 1 minus the rate. A 20% decrease on 250 is 250 × 0.80 = 200.

What is the difference between the two modes?

"% change between two values" tells you the percentage that separates an old and new number. "Apply a % increase or decrease" goes the other way — you give a starting number and a percentage, and it returns the resulting value.

Can I chain two percentage changes?

Not in one step, and be careful — a 10% rise followed by a 10% fall does not return to the start. 100 → 110 → 99, a net 1% drop, because the second percentage applies to the larger figure.

Is my data sent anywhere?

No. The calculator is privacy-first — every figure stays in your browser and nothing is transmitted to any server.

Percentage Increase / Decrease Calculator

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

All arithmetic happens locally in your browser, so the numbers you enter never leave your device.