Three percentage tools in one page: find a percentage of a number, figure out what percent one number is of another, and measure percentage increase or decrease. Leave any one box blank and it’s solved for you automatically — everything updates live as you type, right in your browser.
Percentage of a number
X is what percent of Y
Percentage increase or decrease
How it works
Each section is a live equation with three numbers — fill in any two and the third is computed the moment you leave it blank. “Percent of” multiplies (15% of 80 = 0.15 × 80 = 12), “is what percent” divides (12 is what percent of 80 = 12 ÷ 80 = 15%), and the change tool divides the difference by the starting value: going from 80 to 100 is a 25% increase; back from 100 to 80 is a 20% decrease. That asymmetry trips up a lot of mental math, which is exactly why the tool shows both the percentage and the raw difference.
Everyday examples
Tips: 18% tip on a $64.50 bill → 11.61. Sale prices: a $240 jacket at 30% off saves you $72. Stats at work: “up to what percent” questions — 37 of 50 tasks done is 74% complete. Pay raise: $52,000 to $56,500 is an 8.65% increase. Results are computed to full precision and displayed trimmed to six decimals, plenty for everyday use.
Built in-house in plain JavaScript — no widgets, no tracking, nothing you type leaves your device.