Percent Change Calculator

Percent change = (New value − Old value) ÷ Old value × 100. Going from 50 to 65 is a (65 − 50) ÷ 50 × 100 = 30% increase. A negative result means a decrease.

Percent change is directional and always measured relative to the original (old) value — going from 50 to 100 is a 100% increase, but going from 100 back to 50 is only a 50% decrease, even though the dollar or unit change is the same. Percent difference (less common) instead measures the gap relative to the average of the two values, treating neither as the 'original.'

New value = Old value × (1 + percent change ÷ 100). A 30% increase on 50 is 50 × 1.30 = 65. For a decrease, use a negative percentage: a 20% decrease on 50 is 50 × 0.80 = 40.

Because percent change is always calculated from a different base each time. A 50% decrease from 100 gives 50, but a 50% increase from 50 only gives back 75, not 100 — you'd actually need a 100% increase to return to the original value. This is a common source of confusion with percentage math.

Percentage difference = |Value A − Value B| ÷ ((Value A + Value B) ÷ 2) × 100. Unlike percent change, it treats neither value as the 'original' — it's symmetric, so comparing A to B gives the same result as comparing B to A. Use this when you're comparing two independent measurements rather than tracking a before/after change.