How to Calculate Percentage Change (Formula + Examples)
To calculate percentage change, use (new − old) ÷ old × 100. A positive result is an increase; a negative one is a decrease. Example: going from 80 to 100 is (100 − 80) ÷ 80 × 100 = 25% increase. Here's the formula broken down, worked examples, and a free percentage change calculator that does it instantly.
The percentage change formula
Percentage change = (new value − old value) ÷ old value × 100
The key — and the part everyone gets wrong — is dividing by the original (old) value. The change is always measured relative to where you started, not where you ended up.
Worked examples
- Price rise: $50 → $65. (65 − 50) ÷ 50 × 100 = +30%
- Weight loss: 200 lb → 180 lb. (180 − 200) ÷ 200 × 100 = −10%
- Traffic growth: 1,200 → 3,000 visits. (3,000 − 1,200) ÷ 1,200 × 100 = +150%
Check any of these in the Percentage Change Calculator — enter the old and new values and it shows the result and direction automatically.
Percentage increase vs percentage decrease
Both use the same formula — the sign tells you which. A positive result is a percentage increase; a negative result is a percentage decrease. In writing, people usually quote the absolute value and add the direction in words ("a 10% drop").
Percentage change vs percentage difference
Percentage change has a clear before and after, so you divide by the original value. Percentage difference compares two values with no natural "start", so you divide by their average: |A − B| ÷ ((A + B) ÷ 2) × 100. Use change for growth over time, difference for comparing two unrelated figures.
A common trap: increases and decreases aren't symmetric
Go from 100 to 150 and that's a +50% increase. Go back from 150 to 100 and it's only a −33% decrease — because the starting value changed. It's the same reason a stock that drops 50% must then gain 100% just to break even.
Related everyday percentage math
- "What is X% of Y?" or "X is what percent of Y?" — the Percentage Calculator handles all three variations.
- Sale prices: find the final price after a markdown with the Discount Calculator.
Bottom line
Subtract old from new, divide by the old value, multiply by 100 — positive is up, negative is down. Or skip the arithmetic and use the free calculator.