Percent Change Calculator (Increase, Decrease & Percent Error)

Use this free percent change calculator to compare two values. In percent change mode it finds the percent of increase or decrease from an old value to a new one. In percent error mode it compares a measured value to the actual value. Either way you get the percentage, the amount of change, and the full working.

How to use the calculator

1. Pick a mode: percent change or percent error.
2. Enter the two values.
3. Read the percentage, whether it’s an increase or decrease, and the step-by-step calculation.

The formulas

Percent change = (new − old) / |old| × 100%. A positive result is an increase; a negative result is a decrease. Percent error = |measured − actual| / |actual| × 100%.

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Frequently asked questions

How do you calculate percent increase?

Subtract the old value from the new value, divide by the old value, and multiply by 100. Going from 80 to 100 is a 25% increase.

What is percent error?

It measures how far a measured value is from the true value: |measured − actual| / |actual| × 100%. Measured 9.8 vs actual 10 is a 2% error.

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What if the original value is zero?

Percent change is undefined when the original value is 0, because you can’t divide by zero. The tool flags this.

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Read the full lesson: learn the method step by step.

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