Percentage Change Calculator
Find the percentage increase or decrease between two numbers, whatever they represent: a price, a population, a score, a measurement. Enter a starting value and a new value to get the change, clearly labeled as an increase or decrease.
- Percentage Change
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- Absolute Change
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Assumptions
- Percentage change is undefined when the starting value is zero, since that requires dividing by zero. This calculator shows an error rather than a nonsensical result in that case.
- When the starting value is negative, increase and decrease still follow the standard mathematical definition (whether the new value is greater or less than the old one), which can invert what feels intuitive. Going from -100 to -50 counts as a 50% increase by this math, even though both numbers are negative.
- Percentage change and percentage point change are different measurements. If you're comparing two percentages, such as a rate moving from 20% to 25%, decide whether you want the percentage point difference (5 points) or the percentage change relative to the starting rate (25%), since both are valid but answer different questions.
- The Census and BLS sources below are cited for their definitions and examples as reported through search results; direct verification of both pages was blocked by a 403 response on every attempt (confirming the government domains are live, not that the specific content was independently confirmed). The formula itself is standard arithmetic, not dependent on either source.
Sources
How percentage change is calculated, and why zero and negative values are special
Percentage change is the difference between two values, divided by the absolute value of the starting value, times 100. Dividing by the absolute value rather than the plain starting value is what keeps the direction (increase or decrease) matching whether the new value is actually bigger or smaller, even when the starting value itself is negative. It also means the calculation is impossible when the starting value is exactly zero: dividing by zero has no defined answer, so this calculator flags that case with a plain error message rather than showing an infinite or nonsensical result.
Percentage change versus percentage point change
These two terms get conflated constantly, but they measure different things. A percentage point change is a plain subtraction between two percentages: a rate moving from 20% to 25% is a 5 percentage point increase. A percentage change expresses that same move relative to where it started: the same move from 20% to 25% is a 25% increase (5 divided by 20, times 100), not a 5% increase. Both numbers are correct, they just answer different questions, and mixing them up is one of the most common statistical reporting errors.
Worked example
A value moving from 50 to 65.
Absolute change = 65 - 50 = 15. Percentage change = (15 / |50|) x 100 = 30% increase.
Frequently asked questions
How do I calculate percentage change between two numbers?
Subtract the starting value from the new value, divide that by the absolute value of the starting value, then multiply by 100. This calculator does that automatically and labels the result as an increase or decrease so you don't have to interpret the sign yourself.
How is a percentage increase different from a percentage decrease in the math?
They use the exact same formula. The only difference is the sign of the result: a positive result means the new value is bigger than the starting value (an increase), and a negative result means it's smaller (a decrease). This calculator labels the direction directly instead of leaving you to read a plus or minus sign.
Why does my percentage decrease look different when I swap the two numbers?
Percentage change isn't symmetric, because the starting value is always the denominator. Going from 100 to 50 is a 50% decrease, but going from 50 back to 100 is a 100% increase, not another 50%. The starting point changed, so the base the percentage is measured against changed too.
Is percent change the same as percent difference?
No. Percent change always has a clear starting point and ending point, and measures the move relative to the start. Percent difference typically treats two values symmetrically, often comparing them against their average, since neither one is designated as the original. Use percent change when one value genuinely came before the other in time or sequence, like a price before and after a sale.
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