How to Calculate Percentage Increase (or Decrease)
Percentage increase and decrease show how much something has changed relative to where it started — a price rise, audience growth, a pay increase, a drop in sales. The formula is simple once you know it. This guide shows how to calculate percentage increase (and decrease) with examples and a free calculator.
📈 Try the Percentage Calculator now — freeOpen →Percentage change is how we compare growth and decline fairly across different sizes. Knowing the formula lets you understand price changes, track growth, and sanity-check statistics — and avoid the common errors that trip people up.
The percentage change formula
Subtract the old value from the new value, divide by the old value, and multiply by 100. If a price rises from 50 to 65: (65 − 50) ÷ 50 × 100 = 30% increase. If followers drop from 200 to 150: (150 − 200) ÷ 200 × 100 = −25%, a 25% decrease.
The key is always dividing by the original (old) value — that's the base you're measuring change against. A negative result means a decrease.
The common trap
A percentage increase and the same percentage decrease do not cancel out. If something goes up 50% then down 50%, you don't return to the start — because the decrease is calculated from a larger base. Up 50% from 100 is 150; down 50% from 150 is 75, not 100.
This trips people up constantly with prices and investments. The calculator handles it correctly, but the lesson is: always measure change against the current base, not the original.
Step-by-step
Common mistakes to avoid
Pro tips
Frequently asked questions
How do I calculate percentage increase?
Subtract the old value from the new, divide by the old value, and multiply by 100. From 50 to 65 is (65−50)÷50×100 = 30%.
How do I calculate percentage decrease?
The same formula — a negative result is a decrease. From 200 to 150 is −25%.
Do a rise and equal fall cancel out?
No — the fall is calculated from a larger base, so up 50% then down 50% leaves you below where you started.
Is the calculator free?
Yes — free with no sign-up, and it runs instantly in your browser.
Which value do I divide by?
Always the original (old) value — that's the base you're measuring the change against.
Percentage change is (new − old) ÷ old × 100 — always divide by the original value, and a negative result is a decrease. Remember that a rise and an equal fall don't cancel out. Master that and you'll read any change correctly. Free calculator in your browser.