Three percentage questions cover almost every everyday situation: what is 15% of 200, 45 is what percent of 150, and what is the percent change from 80 to 100. This calculator answers all three — pick a mode, type two numbers, and the result appears as you type, with the full sentence spelled out so you can sanity-check it. It’s free, needs no signup, and the URL updates as you go, so you can share a link that reopens with your exact numbers.
How to use
- Pick the mode that matches your question using the three buttons.
- Type your two numbers — decimals and negative values are fine.
- Read the result below; it recalculates as you type, rounded to two decimal places.
- Copy the address-bar URL if you want to share or save the calculation — it reopens with your mode and numbers already filled in.
Tips, discounts, and score changes
The “What is X% of Y?” mode is the workhorse: an 18% tip on a $64 bill (X = 18, Y = 64 → $11.52), a 30% discount on a $250 jacket ($75 off, so $175 to pay), or the 6.5% sales tax on a purchase. The “X is what % of Y?” mode runs the other direction — 42 correct answers out of 60 questions is 70%, and $840 spent from a $1,200 budget is 70% used. The percent change mode compares before and after: a stock that moves from $80 to $100 gained 25%, a rent increase from $1,500 to $1,650 is +10%, and a test score that drops from 90 to 81 fell 10%. If you’re tracking a change over a specific period, our date difference calculator tells you exactly how many days that period covers.
The mistake percent change punishes
Percent change is always relative to the starting value, and that trips people up in both directions. A 50% loss needs a 100% gain to recover, because the base shrank. A price that rises 10% and then falls 10% ends below where it started (100 → 110 → 99). And comparing two percentages — say a conversion rate going from 2% to 3% — is a +50% change but only one percentage point. When a headline says something “doubled”, check the base: from the change mode here, doubling is always exactly +100%, no matter the numbers. If the starting value is zero, no percentage exists at all — the calculator says so rather than inventing one.
Limits
- Results display rounded to two decimal places; the underlying math is full floating-point precision, so chained rounding errors don’t accumulate inside a single calculation.
- Percent change from a starting value of zero is undefined and shows a message instead of a number, as does “X is what % of 0”.
- This tool works on plain numbers — it doesn’t add currency-specific rounding rules, so for multi-step money calculations round only at the end.
- Extremely large inputs are capped at one trillion to keep results readable.
Everything runs client-side: the numbers you type are never sent or stored. Explore the rest of our calculators for the same instant, private experience — the age calculator turns a birth date into an exact age the same way — or browse the file tools that process PDFs and images without uploading them.