Compare an old value with a new value
Enter the starting amount as Old value and the ending amount as New value, then select Calculate. Both must describe the same quantity in the same units. The old value must be positive; the new value can be zero.
Try example fills 80 and 100 without calculating. Reset clears both values. Editing either value removes the previous result until you calculate again.
Formula and examples
Percentage change = (new value − old value) ÷ old value × 100
The Bureau of Labor Statistics describes this calculation using the earlier value as the denominator. The result is positive for an increase and negative for a decrease. The percent symbol represents 0.01, as explained in NIST’s guide.
| Old value | New value | Percentage change | Absolute difference |
|---|---|---|---|
| 80 | 100 | 25% increase | 20 |
| 100 | 80 | −20% decrease | 20 |
| 80 | 80 | 0% | 0 |
| 80 | 0 | −100% | 80 |
| 3 | 4 | 33.3333%, rounded | 1 |
For 80 to 100, the increase is 20 and 20 ÷ 80 × 100 = 25%. Reversing the values changes the base: −20 ÷ 100 × 100 = −20%. Equal numerical differences can therefore produce different percentage changes.
The Change (new − old) keeps its sign. The Absolute difference is the size of that change without a sign. Both are in the units entered.
Limits and rounding
Enter values up to 1,000,000,000,000, with at most six decimal places. Use a decimal point, without commas or unit symbols. Scientific notation is not accepted. A zero old value would require division by zero; negative old values are outside this tool’s scope.
Percentage results are rounded to at most four decimal places. Halfway values round away from zero: 0.00005% becomes 0.0001%, and −0.00005% becomes −0.0001%. An even smaller change may display as 0%; its direction and exact numerical difference remain visible. Differences are calculated from the entered decimal values without intermediate rounding.
Percentage change or percentage points?
A rate rising from 10% to 15% has increased by 5 percentage points and by 50% relative to its old value. Entering 10 and 15 here returns the relative 50% increase.
If neither value is the starting point, use the Percentage Difference Calculator to compare two positive values against their average. To find a percentage of one amount, use the Percentage Calculator.