Percentage calculator
MathNo. 10 / 24approved
Four classic operations: a percentage of a number, one number as a percentage of another, percentage change, and add or subtract a percentage. All live.
percentages are opinions with decimals. we just make the decimals honest.
work surface
Math, not advice — results are indicative. Read the disclaimer.
most-used utilities
Restaurant tip
20% on a €45 dinner. Generosity, calculated before the card leaves your hand.
Test score
42 out of 60. Is it passing? Math says yes. Emotionally, it's complicated.
Salary raise
A 12% raise on €1,800. Update your email signature accordingly.
Price drop
€120 down to €90. Your wallet applauds, quietly.
pro tips
A 10% increase followed by a 10% decrease is not zero — it's 1% less. Percentages lie in chains.
Quick mental math: 10% is just moving the decimal, 5% is half of that, and tips are the reason you're here.
Divide by 100 to get 1%, then multiply. That's the whole trick — no one warns you it's this easy.
When a sale says "up to 70% off", exactly one item is at 70% off. Calculate before you queue.
what it does
Four classic operations in one place: what a percentage of a number is, what percent one number is of another, how much something changed, and how to add or subtract a percentage. Everything updates as you type — no button, no judgement, no "carry the one".
What is slices a piece off a number, what percent compares two numbers, change measures the journey between them, and add or subtract grows or shrinks a number by a percentage. Each mode shows only the inputs it needs — no math graveyard.
Pick a real scenario from the cards above and it fills itself in. Perfect for tips, grades, raises, VAT and sale prices — the four horsemen of adult arithmetic.
Every result comes with the formula that made it, because trusting a number without knowing where it came from is how people end up paying 30% more for a "15% discount".
quick answers
Which mode should I use?
"What is" finds a part of a number, "what percent" compares two numbers, "change" measures the journey between them, and add/subtract grows or shrinks by a percentage. Pick the question you're actually asking.
How do I calculate percentage change?
Subtract the old value from the new, divide by the old, multiply by 100. The widget does it live — the formula sits right under the result.
How is a tip a percentage?
A tip is a percentage of the bill: 20% on $45 is $9. Tipping culture varies wildly; the calculator doesn't judge.
Are the results rounded?
Yes — to two decimals, which is about as precise as money usually needs to be.