Two numbers in, one percentage out
Say your rent went from $1,200 to $1,380. By how much did it actually climb? Drop both numbers in and you get the answer: 15% increase. The math is (to - from) / from x 100, and the sign tells you which way things moved. Positive means up, negative means down, and the calculator spells out the word so you never second-guess it.
That formula trips a lot of people up because of the denominator. The percent change is always measured against where you started, not where you ended. Going from 100 to 150 is a 50% increase. But going back from 150 to 100 is only a 33.3% decrease, because now you’re dividing by 150. Same two numbers, different base, different answer. The calculator handles that automatically.
The other mode: apply a percent
Flip to the second tab and the question reverses. Now you have one number and a percentage, and you want the result. A jacket is $80 and there’s a 15% restocking fee, what do you actually pay? Pick “increase,” enter 80 and 15, and you get $92. Need to knock 30% off a $250 invoice instead? Switch the toggle to “decrease” and you’ll see $175.
This side runs on value x (1 ± percent/100). It’s the everyday version, the one you reach for when adding a tip, marking up a quote, or trimming a budget line. Both the amount of the change and the final figure show up, so you can sanity-check the piece you care about.
Where this gets used
Percent change shows up constantly once you start noticing it:
- Salary bumps. Your raise went from $62k to $67k. That’s an 8.06% increase, which is the number worth knowing before your next review.
- Price tracking. A part you buy regularly jumped from $4.50 to $5.10. The reverse mode confirms it’s a 13.3% hike, not the “tiny bump” the supplier called it.
- Stats and reports. Traffic, weight, temperature, headcount, anything that moves over time gets described as a percent change.
- Reverse-engineering a markup. Cost is $40, list price is $60. The change mode tells you that’s a 50% markup on cost.
One thing to keep straight: percent change and percentage points are not the same animal. If a rate goes from 5% to 7%, that’s a 2 percentage-point rise, but a 40% increase in relative terms. This tool gives you the relative figure. For the points, you just subtract.
Questions people ask
How do I calculate percent increase by hand?
Subtract the old value from the new one, divide by the old value, then multiply by 100. So from 200 to 250: (250 - 200) / 200 x 100 = 25%.
Why is a decrease percentage smaller than the matching increase?
Because the base changes. Up from 100 to 200 is +100%, but down from 200 to 100 is only -50%. You’re dividing by the starting number each time, and the starting numbers differ.
Can I get a percentage over 100%?
Yep. If something triples from 50 to 150, that’s a 200% increase. There’s no upper limit on increases. Decreases, though, bottom out at -100% (when the value hits zero).
What if my starting value is zero?
Then percent change is undefined, since you’d be dividing by zero. Going from 0 to anything is technically an infinite increase. Use the “apply a percent” mode instead if you have a base to work from.
Does this round the results?
The percentage shows up to two decimals and the computed values up to four, with trailing zeros stripped so ratios stay clean. Nothing’s truncated behind the scenes; what you see is the real number, just tidied.