Percentage Change Calculator
Compare an original value with a new one and see the percentage change, the difference, and whether it went up or down.
Percentage Change Calculator calculates in your browser.
Measure how much a value changed
Use this when you have a before and an after — last month’s sales and this month’s, an old price and a new one, a test score before and after practice. You get the change as a percentage of the original value, the plain difference, and whether it was an increase, a decrease, or no change, written out in words rather than signalled by color alone. It also handles the two cases that trip up most percentage-change calculations: a starting value of 0 and a negative starting value.
How to use the Percentage Change Calculator
- Type the original (before) value.
- Type the new (after) value. Use the ± button if either value is negative and your keypad has no minus key.
- Read the percentage change, the change, and the direction. Copy Result copies a line such as “From 100 to 125: +25% (an increase of 25)”.
The formula
percentage change = (new value − original value) ÷ original value × 100
The original value is the yardstick: the difference is measured as a share of where you started. That is why the order matters — 100 → 125 is +25%, but 125 → 100 is −20%, because the same difference of 25 is compared with a different starting value. Percentages are shown to up to 4 decimal places, so 3 → 4 shows as +33.3333%.
| Values | Percentage change | Change | Direction |
|---|---|---|---|
| 100 → 125 | +25% | +25 | Increase |
| 100 → 75 | -25% | -25 | Decrease |
| 80 → 80 | 0% | 0 | No change |
| 3 → 4 | +33.3333% | +1 | Increase |
| 50 → 150 | +200% | +100 | Increase |
| 0 → 50 | Undefined | +50 | Increase |
| -50 → -25 | -50% | +25 | Increase |
Starting from zero or a negative number
When the original value is 0, the formula would divide by zero, which has no answer. Going from 0 to 50 is a real change of 50, but there is no percentage that describes it, so the calculator shows “Undefined” for the percentage, still shows the change, and explains why — it never shows Infinity or NaN.
When the original value is negative, the calculator keeps the standard formula exactly as written, and the result can look backwards: from −50 to −25 the value went up by 25, yet (−25 − (−50)) ÷ (−50) × 100 = −50%. Dividing by a negative number flips the sign. The direction is always shown separately in words, and a note appears whenever the percentage’s sign and the direction disagree.
Calculated on your device
- The calculation runs in your browser as you type; nothing is sent to a server.
- The values and results are not sent to Looty Tools or stored.
- Refreshing the page clears the boxes.
Limitations
- Percentage change from 0 is undefined, so only the change is shown in that case.
- With a negative original value the standard formula is used unchanged. Some fields divide by the absolute value of the original instead; that convention is not used here, so compare with what your source expects.
- This is percentage change from a starting value — not percent difference (which divides by the average of the two values) and not percentage points (the plain difference between two percentages).
- Values can be up to 1,000,000,000,000,000 with up to 10 decimal places; percentages are shown to up to 4 decimal places.
Related calculators
- Percentage CalculatorFind a percentage of a number.
- Percentage Increase CalculatorIncrease a number by a percentage.
- Percentage Decrease CalculatorDecrease a number by a percentage.
Guides
- Calculate Percentage ChangeThe percentage change formula with worked examples, how to read positive and negative results, a spreadsheet formula, and checks that catch errors.
- Change From Zero or NegativeWhy percentage change from zero is undefined, why a negative starting value can flip the sign, and how to report these changes honestly.
- Change vs. DifferenceWhen to measure from a starting value and when to compare two values side by side, the percent difference formula, and where percentage points fit.
Percentage Change Calculator FAQ
- What is the formula for percentage change?
- (new value − original value) ÷ original value × 100. From 100 to 125 that is 25 ÷ 100 × 100 = +25%; from 100 to 75 it is −25%.
- Why is percentage change from 0 undefined?
- The formula divides by the original value, and dividing by zero has no answer. Going from 0 to 50 is a real change of 50, but there is no percentage to attach to it, so the calculator shows the change and marks the percentage as undefined instead of showing Infinity.
- What happens when the original value is negative?
- The calculator applies the standard formula as it is, which makes the sign of the percentage the opposite of the direction: from −50 to −25 the value went up by 25, but the formula gives −50%. The direction is always shown separately in words, with a note explaining the sign. Some fields use other conventions for negative starting values, so check which one your context expects.
- Is percentage change the same as percent difference?
- No. Percentage change measures from a starting point, so direction matters: 100 → 125 is +25%, but 125 → 100 is −20%. Percent difference compares two values without a starting point by dividing by their average, so both ways give about 22.22%.
- Can percentage change be more than 100%?
- Increases can: 50 to 150 is +200%. A fall from a positive value to 0 is −100%, and it only goes beyond −100% if the new value is below zero, such as 100 to −50 (−150%).
- What is the difference between the change and the percentage?
- The change is the plain difference, new minus original, in the same units as your values. The percentage expresses that difference relative to the original value.
- Are the numbers I enter sent anywhere?
- No. The calculation runs in your browser as you type. The numbers you enter and the results are not sent to Looty Tools or stored; refreshing the page clears them.
