Percentage Change Calculator: Increase, Decrease & Formula

Percentage change formula

Percentage change = (new value − original value) ÷ original value × 100. A positive result means an increase; a negative result means a decrease. The original value is the denominator because the change is measured relative to where the value started.

Do not reverse the original and new values. Changing the denominator changes the answer and can make a decrease look like a different percentage from the reverse increase.

Worked examples: increase and decrease

If a price rises from 80 to 100, the difference is 20. Divide 20 by the original 80 and multiply by 100: the increase is 25%.

If a value falls from 100 to 80, the difference is −20. Divide −20 by the original 100 and multiply by 100: the change is −20%, meaning a 20% decrease. The reverse movement is not the same percentage because the starting value is different.

Why reverse changes have different percentages

A change from 100 to 120 is a 20% increase because the difference of 20 is divided by the original 100. Reversing the movement from 120 to 100 is a 16.67% decrease because the same difference is now divided by 120.

This is why a 20% increase followed by a 20% decrease does not return to the starting value: 100 rises to 120, then falls to 96. Always use the value at the start of the specific comparison as the denominator.

Use forward and reverse calculation modes

For a normal comparison, enter the original value and new value to calculate the percentage increase or decrease. Both values must use the same unit, and the original value cannot be zero.

To work backwards, choose the reverse mode, enter the final value and the known percentage change, then calculate the original value with: original = final value ÷ (1 + percentage change ÷ 100). For example, a final value of 120 after a 20% increase means the original value was 100. A change of −100% or less cannot be reversed with this formula because it implies a zero or negative multiplier.

Percentage change versus percentage points

Percentage change is a relative change between two values. Percentage points describe the arithmetic difference between two percentages. For example, a rate moving from 10% to 12% has increased by 2 percentage points, while its relative percentage change is 20%.

Use percentage points when comparing rates such as interest, market share or pass rates. Use percentage change when you want to express the relative movement from an original numerical value.

Frequently asked questions