How this calculator works
This calculator works out how much a value went up or down, as a percentage of where it started. Use it for price rises, salary changes, website traffic, weight loss or any before-and-after comparison.
Subtract the starting value from the new value, divide by the starting value, then multiply by 100. A positive result is an increase and a negative result is a decrease.
Worked example: rent going from $1,200 to $1,320
- Find the change: 1,320 − 1,200 = 120.
- Divide by the starting value: 120 ÷ 1,200 = 0.1.
- Multiply by 100: 0.1 × 100 = 10.
The rent went up by 10%.
Quick reference: changes from a starting value of 80
| Before | After | Change |
|---|---|---|
| 80 | 60 | 25% decrease |
| 80 | 72 | 10% decrease |
| 80 | 84 | 5% increase |
| 80 | 88 | 10% increase |
| 80 | 100 | 25% increase |
| 80 | 120 | 50% increase |
| 80 | 160 | 100% increase |
Common mistake
Thinking a rise and a fall of the same percentage cancel out. If a $100 price rises 10% to $110 and then falls 10%, it ends at $99, not $100, because the second 10% is taken from a bigger number.
Questions people ask
- Which number is the “starting value”?
- The older or original number, the one you are comparing from. The percentage is always measured against it.
- Can a decrease be more than 100%?
- Not for things that can't go below zero, like prices. A drop to zero is a 100% decrease. An increase, however, has no upper limit.
- Why can't the starting value be zero?
- Because you can't divide by zero. Going from 0 to anything has no meaningful percentage change.
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