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Percent Change Calculator

Find the percentage increase or decrease between two values.

How it is calculated

Percentage change compares a new value with an old one relative to the old value: change % = (new − old) / |old| × 100. The tool also shows the absolute difference, new − old, in the same unit as your numbers. A positive result is an increase and a negative one a decrease. The old value is the reference, so it cannot be zero, and in that case nothing is shown. Using the absolute value of the old number keeps the sign meaningful when it is negative. Results have two decimals. The percentage is relative to the starting point, which is why a rise and a fall of the same size give different percentages.

Worked example

A price moves from 80 to 100. Difference: 100 − 80 = 20.00. Divide by the old value: 20 / 80 = 0.25. Multiply by 100 to get 25.00%. So the price rose by 25.00%. If it then falls back from 100 to 80, the change is −20 / 100 = −20.00%, so going up 25% and down 20% brings you back to the start.

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Common mistakes

  • Using the new value as the base: 20 / 100 is 20%, not the 25% increase from 80.
  • Confusing percent change with percentage points: moving from 10% to 12% is +2 points but a 20% relative change.
  • Averaging percentage changes over several periods instead of compounding them.
  • Entering old and new values in swapped order, which flips the sign of the result.

About this calculator

This calculator finds the percentage change between an old value and a new value using the formula ((new − old) / old) × 100. A positive result means an increase, a negative result means a decrease — the sign is preserved so you can tell growth from decline at a glance.

It's the standard way to compare prices, stock quotes, populations, salaries, or any two numbers that change over time, and it's used constantly by analysts tracking revenue growth, shoppers comparing sale prices, and students checking homework on percentages. Because it divides by the old value, the tool also handles the common pitfall of confusing percent change with percentage-point change, which trips people up when comparing rates like interest or tax percentages.

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