Percentage Calculator
Percents of, what-percent, change and increase — four modes, live
The most abused number in public
Percentages feel simple and mislead constantly: discounts stack multiplicatively not additively, a pay cut and equal raise don't cancel, and percentage points are not percents. Four tiny formulas cover nearly every daily encounter — this page runs all four live.
What this tool does
- 💯 X% of Y with instant answers
- 📊 What percent X is of Y
- 📈 Percent change between two numbers
- ➕ Increase or decrease a base by a percent
When to use it
- Sale tags: 30% off 89, twice
- Tips, taxes and fees on a bill
- Reading poll swings and price moves honestly
Privacy: pure arithmetic in your browser — numbers you type never leave your device.
Last updated · 2026-09-01
How the math works
Four closed forms: p·b/100, (a/b)·100, ((b−a)/|a|)·100, b·(1+p/100). Division by zero yields a clean empty state instead of Infinity leaking into the page.
Why percent here?
Four modes, zero tabs
Percent-of, what-percent, change and increase live on one page updating as you type — the four questions people actually ask, no mode-hunting.
Honest rounding
Two-decimal display with full-precision internals, so 33.333…% of 90 reads 30 without pretending the math underneath is fuzzy.
Teaches while answering
The FAQ explains points-vs-percent and the asymmetric round trip — the two traps this tool exists to defuse.
Frequently asked questions
What is the difference between percent and percentage points?⌄
A move from 20% to 25% is a 5 percentage-point move but a 25% relative increase. Politics and finance exploit this confusion constantly — the change mode shows the relative figure; subtract for points.
Why is a 50% drop followed by 50% gain not break-even?⌄
Because the base changes: 100 → 50 (−50%), then 50 → 75 (+50%). Percentages always apply to their own base — use the increase mode to see it.
How is the math done?⌄
Plain arithmetic with two-decimal display rounding. No compounding, no annualizing — what you see is exactly the formula stated above each result.
Frequently asked questions
What is the difference between percent and percentage points?
A move from 20% to 25% is a 5 percentage-point move but a 25% relative increase. Politics and finance exploit this confusion constantly — the change mode shows the relative figure; subtract for points.
Why is a 50% drop followed by 50% gain not break-even?
Because the base changes: 100 → 50 (−50%), then 50 → 75 (+50%). Percentages always apply to their own base — use the increase mode to see it.
How is the math done?
Plain arithmetic with two-decimal display rounding. No compounding, no annualizing — what you see is exactly the formula stated above each result.
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