A percent change tells you how much a number has grown or shrunk relative to its starting point. Whether you are tracking a stock price, comparing this month's sales to last month's, checking a raise at work, or reading a news headline about inflation, the question is always the same: by what percentage did the value move? This percent change calculator takes your original value and your new value and returns the percentage increase or decrease, the absolute difference, the ratio between the two, and the reverse change you would need to get back to where you started.
Type your two numbers and the result updates instantly. Because percent change is easy to misread, the card also spells out the direction in plain words and shows why a +25% increase is not undone by a -25% decrease.
How to Use
- Enter the Original (Old) Value — the number before the change. This is the base that the percentage is calculated against. It cannot be zero, because dividing by zero is undefined.
- Enter the New Value — the number after the change. This can be larger or smaller than the original; the calculator handles both.
- Set the Number of Periods (Years). If the move happened in a single step, leave it at 1 and the annualized rate equals the total change. If you are comparing a stock price or revenue over several years, enter the number of years and the calculator also shows the annualized compound growth rate (CAGR).
- Read the Percent Change line. A positive number is a percentage increase; a negative number is a percentage decrease. The Direction line prints 1 for an increase (new value higher than old), 0 for flat (no change), or −1 for a decrease (new value lower than old) — read it as "Increase / Flat / Decrease" so you do not have to interpret the sign of the percent alone.
- Look at the Signed Difference to see the plain gap between the two values in your own units, and at the New / Old Ratio to see the new value as a multiple of the old one.
- Check the Change to Return to Old Value line. This shows the opposite percent move needed to go from the new value back to the original. It is almost never the same number as the first result, which is the whole point of the asymmetry note below.
You can enter any real numbers — prices, counts, scores, temperatures, weights. The formula does not care about the unit, only the ratio between the two values.
The Percent Change Formula
Percent change compares the gap between two numbers to the starting number:
Percent Change = ((New Value − Original Value) ÷ Original Value) × 100
Where:
- New Value − Original Value is the absolute difference (positive for a rise, negative for a fall).
- ÷ Original Value rescales that difference relative to the starting point.
- × 100 converts the ratio into a percentage.
Worked example: go from 200 to 250. The difference is 250 − 200 = 50. Divide by the original 200 to get 0.25, then multiply by 100: the result is +25%. That is a 25% increase.
Now reverse the order and go from 250 to 200. The difference is 200 − 250 = −50. Divide by the original 250 to get −0.20, then multiply by 100: the result is −20%. That is a 20% decrease.
Notice the two directions do not cancel to zero. Going up 25% from 200 lands you at 250, but getting back from 250 to 200 takes a 20% drop, not a 25% drop. The base changed, and percentages always live and die by their base.
Why Increases and Decreases Are Not Symmetric
This is the single most common mistake people make with percentages. If a price rises 25%, a 25% cut afterward does not bring it back to the start.
On a $100 item, a 25% raise takes it to $125. To get from $125 back to $100 you need to remove $25 — but $25 is now measured against the larger base of $125, which is only 20%. So the return trip is a 20% decrease. The "Change to Return to Old Value" line on this calculator shows that number explicitly so you never have to guess.
The same logic works in reverse. A 20% drop from 250 leaves 200, and a 25% rise from 200 is what restores 250. Bigger drops need smaller rebounds, and smaller drops need bigger rebounds, because the base after a move is always the new value.
Examples
Example 1 — A salary raise. You were earning $80,000 and now earn $92,000. The difference is $12,000. Divide by the original $80,000: 12,000 ÷ 80,000 = 0.15, so your raise is a +15% increase. To see the reverse, dropping from $92,000 back to $80,000 would be a −13.04% change — not −15%.
Example 2 — A stock price decline. A share trades at $40 and falls to $30. The difference is −$10. Divide by the original $40: −10 ÷ 40 = −0.25, so the drop is a −25% decrease. To climb back from $30 to $40 you need +33.33%, which is why a deep loss hurts to recover.
Example 3 — A large real-world change. A company's quarterly revenue goes from $1,000,000 to $1,250,000. The difference is $250,000 against a $1,000,000 base, which is exactly +25%. The calculator handles numbers at this scale with no loss of precision, and the reverse move back to $1,000,000 is a −20% decrease.
FAQ
How do I calculate percent change between two numbers?
Subtract the original value from the new value, divide that difference by the original value, and multiply by 100. If the result is positive you have an increase; if it is negative you have a decrease. For example, from 200 to 250: (250 − 200) ÷ 200 × 100 = +25%.
What is the difference between percent change and percent difference?
Percent change always has a direction: it measures a move from an old value to a new value, and the old value is the base. Percent difference is symmetric and uses the average of the two numbers as the base, so it is used when neither value is clearly "before" or "after." This calculator is built for the directional old-to-new case.
Why is a 25% increase not canceled by a 25% decrease?
Because the base changes. A 25% rise on 200 adds 50 to reach 250. Undoing that move means removing 50 from 250, and 50 ÷ 250 is only 20%. The calculator's "Change to Return to Old Value" line shows the exact reverse percentage so you can see the asymmetry at a glance.
What if the original value is zero?
Percent change is undefined when the original value is zero, because the formula divides by the original value and division by zero is not allowed. Going from 0 to 1000 looks like an infinite jump, not a meaningful percentage, so the calculator flags it as an error instead of returning a nonsense number.
Can I use negative numbers as inputs?
Yes. The formula works with negative values, but interpret the direction carefully. Going from −200 to −250 is a larger loss, and the math still produces a +25% ratio because both signs cancel in the division. When the base itself is negative, always read the absolute difference and the real-world meaning rather than trusting the sign of the percent alone.
Is percent change the same as percent increase or decrease?
Yes. "Percent increase" is the positive case (new value is larger), and "percent decrease" is the negative case (new value is smaller). This single calculator handles both, and the Direction line tells you which one you are looking at.
Disclaimer
This percent change calculator is provided for informational purposes only and does not constitute financial, investment, accounting, or tax advice. Results are based purely on the two numbers you enter and the standard percent-change formula; they do not account for fees, compounding over time, or rounding in real-world reporting. Always verify figures against your own source documents and consult a qualified professional before making any financial decision.