How to use
- Enter the old (starting) value.
- Enter the new (ending) value.
- Read the percent change. A negative result means the value fell.
Worked example: Rent from $1,250 to $1,340
The change is 1,340 − 1,250 = 90. Divided by the old value, 90 ÷ 1,250 = 0.072, which is a 7.2% increase.
If rent instead dropped from $1,340 to $1,250, the change would be −90 ÷ 1,340 = −6.72%. The same dollar amount is a different percentage because the base changed.
Frequently asked questions
What is the formula?
Percent change = (new − old) ÷ |old| × 100. The absolute value keeps the sign meaningful when the old value is negative.
What if the old value is zero?
The result is not defined, and the calculator says so. Any change from zero cannot be expressed as a percentage.
Why is a 10% rise followed by a 10% fall not back to the start?
Because the second 10% is taken from a bigger number. 100 → 110 → 99. Percent changes do not simply add up.
How do I reverse a percent change?
Old = new ÷ (1 + change ÷ 100). If 110 is after a 10% rise, the old value was 100.
Does this work for negative values?
Yes. From −20 to −10 is a 50% increase: (−10 − (−20)) ÷ 20 × 100.
Is percent change the same as percentage points?
No. From 10% to 15% is a 5 percentage-point rise but a 50% percent change.