Percent Change Calculator
Enter the old value and the new value. The calculator applies the percent change formula — (new − old) ÷ old × 100 — and tells you whether the change is an increase or a decrease.
Example: with Old value 80 · New value 92 → Percent change: +15.00% (increase).
Computed by the calculator below using its default values. Change any input to see your own numbers.
📊 Track your numbers with a budgeting planner
Check it outThe percent change formula, worked through
Percent change compares a new value to an old one, always dividing by the old value: (new − old) ÷ old × 100. If a grocery bill goes from $80 to $92, the change is $12, and 12 ÷ 80 × 100 = +15%. A positive result is an increase, a negative one a decrease — the sign carries the direction, so from 50 down to 40 the formula gives −20%.
Two things trip people up. First, the base: 40 → 50 is +25%, yet 50 → 40 is only −20%, because each change is measured against its own starting point. Second, changes over 100% are perfectly valid — from 20 to 65 is (65 − 20) ÷ 20 × 100 = +225%, meaning the value more than tripled. When the old value is 0, percent change is undefined; report the absolute change instead.
How it’s calculated
Percent change = (new − old) ÷ |old| × 100, with the sign indicating direction: positive = increase, negative = decrease. The absolute change row is simply new − old. Dividing by the absolute value of the old number keeps the direction label correct when the old value is negative, and an old value of 0 returns no result because the change would be undefined.
Results update as you type and are estimates, not professional advice — verify important decisions with a qualified professional.
Common mistakes
- Dividing by the new value instead of the old one — percent change is measured from where you started.
- Dropping the minus sign and calling a decrease an increase; the direction is part of the answer.
- Confusing percentage points with percent change: a rate moving from 4% to 5% is +1 point but a +25% change.
- Averaging percent changes across periods — two months of +10% compound to +21%, not +20%.
Frequently asked questions
How do I calculate percentage change?
Subtract the old value from the new value, divide by the old value, then multiply by 100. From 80 to 92: (92 − 80) ÷ 80 × 100 = +15%.
What does a negative percent change mean?
The value went down. From 50 to 40, (40 − 50) ÷ 50 × 100 = −20%, i.e. a 20% decrease.
Can percent change be more than 100%?
Yes. Anything that more than doubles has a change above +100%: from 20 to 65 is +225%. A decrease, though, can never go below −100% of a positive value, because that means losing everything.
What if the old value is zero?
Percent change from 0 is undefined — you cannot divide by zero. Quote the absolute change instead (e.g. “up 12 units from zero”).
Is percent change the same as percent difference?
No. Percent change uses the old value as the base and has a direction. Percent difference compares two equal-footing values against their average and is always positive.