How to calculate percentage change
Percentage change measures how much a number rose or fell relative to its starting point. First subtract the original value from the new value. Then divide that difference by the original value and multiply by 100. A positive result is an increase and a negative result is a decrease.
For example, a price going from $80 to $100 rises by $20. The relative change is $20 ÷ $80 × 100, or 25%. If a monthly bill falls from $100 to $80, the difference is −$20 and the percentage change is −20%. Reversing a percentage increase does not generally reverse it by the same percentage because the starting base changes.
Why the starting number matters
A change from $10 to $20 is a 100% increase. A change from $100 to $110 is just a 10% increase even though both add $10. That is why percentage change is useful for comparing growth rates across different baselines, such as salary increases, price moves, sales performance, or website traffic.
What happens if the original value is zero?
The usual percentage-change formula divides by the original value. Division by zero is undefined, so the calculator displays a clear explanation instead of a misleading infinite percentage. When only a raw difference is meaningful, compare the absolute values directly.
Percentage points are not percentage change
If a rate moves from 4% to 6%, it has increased by 2 percentage points but by 50% relative to its original level. Use this distinction when discussing interest rates, conversion rates, taxes, or survey results.
Independent educational tool. Calculations are estimates and do not replace a lender statement, payroll advice, tax advice, or legal guidance. Read the disclaimer.