Percentage Increase/Decrease

How percentage increase and decrease work

Percent change measures how much a value grew or shrank relative to where it started. It is the standard way to compare a price rise, a salary bump, or a drop in traffic regardless of the absolute numbers involved.

Formula

Percent change = ((end − start) ÷ start) × 100

A positive result is an increase, a negative result a decrease. When you enter a number of periods, the calculator also shows the compound average change per period (CAGR):

Average per period = ((end ÷ start)^(1 ÷ periods) − 1) × 100

Worked examples

• 80 → 100 — change is 20, so (20 ÷ 80) × 100 = +25%.
• 100 → 75 — change is −25, so −25% (a 25% decrease).
• 100 → 121 over 2 periods — the average is ((121 ÷ 100)^(1/2) − 1) × 100 = 10% per period, because 100 × 1.10 × 1.10 = 121.

Where percent change is used

• Prices and inflation — how much a bill, rent, or grocery basket has risen year over year.
• Pay — the size of a raise, or the real value of a bonus against last year's figure.
• Performance — growth or decline in sales, traffic, followers, or test scores.
• Investments — the return on a holding, and its compound average when spread over several years.

A caveat when the start value is zero or negative

Percent change divides by the starting value, so it breaks down when that start is zero — going from 0 to any number is an infinite percentage, which is why "up from zero" is reported as a plain count, not a percentage. When the start is negative (a loss turning into a profit, say), the sign of the result can be misleading, and the absolute figures usually tell the story more clearly than a percentage.

Note that increases and decreases are not symmetric: a 25% drop from 100 leaves 75, but recovering from 75 to 100 requires a 33.3% rise. For simple "X% of Y" questions, use the percentage calculator.