Percent Change Calculator
How much did this go up or down? Type old and new values, get the percent change.
Find the percentage change between two values, increase or decrease. Useful for raises, sale prices, stock changes, year-over-year revenue, weight loss, anything where you need to know "how much did this go up or down?"
Examples: 80 → 100 = 25% increase · 120 → 90 = 25% decrease · 50 → 50 = 0% change
How percent change is calculated
The formula is straightforward: ((new − old) ÷ old) × 100. The result is the percent change from the old value to the new value. Positive numbers mean an increase, negative numbers mean a decrease.
Why direction matters in the math
Percent change is always relative to the starting value. A 25% increase from 80 takes you to 100. But a 25% decrease from 100 only takes you to 75, not back to 80. That's because the base value changed. Going from 100 to 80 is actually a 20% decrease, not a 25% decrease. This trips people up all the time.
When you'd use this
- Salary raises: what percent raise did I get?
- Sale prices: what percent off is this product?
- Investments: what's my percent return year-over-year?
- Weight changes: what percent of my starting weight have I lost?
- Sales metrics: what's the quarter-over-quarter change?
Edge case: percent change when the old value is zero
Percent change is mathematically undefined when the starting value is zero, you can't divide by zero. If you went from $0 in sales to $1,000 in sales, the percent change is undefined (or in business terms, often described as "infinite growth"). The calculator handles this case by showing the value difference but flagging the percent as undefined.