Percentage Change Calculator
Free percentage change calculator — find the % increase or decrease between two numbers. Perfect for price changes, growth rates, and comparisons. Runs in your browser.
Enter an old value and a new value. The calculator returns the percentage change — how much the value increased or decreased as a percentage of the starting point.
Formula
% change = (new value − old value) ÷ |old value| × 100
The denominator is the absolute value of the starting number, so the formula works for negative starting values too. The sign tells you the direction: positive is an increase, negative is a decrease, zero means no change.
Worked examples
Price went from $100 to $125:
(125 − 100) ÷ 100 × 100 = 25% increase
Price dropped from $125 to $100:
(100 − 125) ÷ 125 × 100 = −20% (20% decrease)
Revenue stayed at $50:
(50 − 50) ÷ 50 × 100 = 0% change
Change vs. difference vs. increase/decrease
These terms get confused a lot in search. Here’s the distinction:
- Percentage change: (new − old) / |old| — the one this calculator does. Compares one quantity at two different times.
- Percentage difference: |A − B| / ((A + B) / 2) — compares two quantities without a time direction. Used when neither is the “starting point.”
- “Percent of”: what our percentage calculator covers — “what is X% of Y?” or “X is what % of Y?”
When someone asks “what percent increase is 100 to 125?” they want percentage change. When they ask “125 is what percent of 100?” they want the percentage calculator. Knowing which is which saves you from getting the wrong answer from the right tool.
Worked examples
-
100 to 125 — 25% increase
25% increase
-
125 to 100 — 20% decrease
20% decrease
-
50 to 50 — no change
0% change
Frequently asked questions
What is percentage change?
Percentage change measures how much something changed relative to where it started. Formula: (new value - old value) / |old value| x 100. A positive result means an increase; a negative result means a decrease.
How is this different from percentage difference?
Percentage change compares one value across time (e.g. price went from $100 to $125 — that's a 25% increase). Percentage difference compares two values as a fraction of their average, usually used when there's no clear 'before' and 'after' (e.g. comparing two test scores). This calculator does percentage change, not percentage difference.
How is this different from the percentage calculator?
Our percentage calculator answers questions like 'what is 20% of 150?' or '45 is what % of 200?' This percentage change calculator answers the time-direction question: 'how much did it change, as a percentage of where it started?' Use this for price changes, growth rates, and before/after comparisons.
What if the old value is negative?
The formula uses the absolute value of the old value as the denominator. If revenue went from -$1,000 (a loss) to +$500 (a profit), that's a 150% increase: (500 - (-1000)) / 1000 x 100 = 150%. The sign of the result still tells you direction clearly.
What if the old value is zero?
Percentage change from zero is mathematically undefined — you can't express a change as a fraction of zero because zero has no magnitude. If a startup had $0 revenue last year and $1,000 this year, the arithmetic answer is 'infinite % increase,' which doesn't help anyone. This calculator returns an error for old value = 0.