Percentage Calculator
Answer the three most common percentage questions instantly — everything runs in your browser.
What is X% of Y?
Calculated locally in your browser.
X is what percent of Y?
Calculated locally in your browser.
Percentage change from A to B
Calculated locally in your browser.
How to use
- Pick the card that matches your question — each card solves one type of percentage problem.
- Type your numbers into the blanks. The result appears instantly as you type; there is no submit button.
- Use Copy to copy a result, or change the numbers to recalculate.
Examples
Tip: what is 15% of $64?
Type 15 and 64 into “What is X% of Y?”. The result is 9.6, so a 15% tip on a $64 bill is $9.60.
Quiz score: 42 out of 60 as a percent
Type 42 and 60 into “X is what percent of Y?”. 42 ÷ 60 × 100 = 70, so the score is 70%.
Price change: from $80 to $92
Type 80 and 92 into the percentage change card. The difference is +12, which is a 15% increase.
Tip, VAT and service charge
Korean prices are usually quoted with VAT included, but restaurant and hotel bills sometimes add 10% VAT and a 10% service charge separately. Applied one after the other on a 100,000 KRW base that is 121,000, not 120,000, because the service charge is calculated on the VAT-inclusive amount. Whenever two percentages stack, apply them in sequence rather than adding the rates together.
Working backwards from a total
If a receipt shows 110,000 KRW including 10% VAT, the pre-tax amount is not 99,000. Divide instead of subtracting: 110,000 ÷ 1.1 = 100,000, and the VAT portion is 10,000. Subtracting 10% from the total is the single most common percentage mistake, and it gets worse as the rate rises.
Interpreting a survey result
Percentages describe a base, and the base is easy to lose. Forty percent of 250 respondents is 100 people; forty percent of the 80 who answered a follow-up is 32. When comparing two percentages, check they share the same base before treating the gap as meaningful.
FAQ
How do I calculate X percent of a number?
Divide the percentage by 100 and multiply by the number: X% of Y = (X ÷ 100) × Y. For example, 25% of 80 = 0.25 × 80 = 20.
How do I work out what percent one number is of another?
Divide the part by the whole and multiply by 100: (part ÷ whole) × 100. For example, 30 out of 120 is (30 ÷ 120) × 100 = 25%.
How is percentage change calculated?
Percentage change = (new − original) ÷ |original| × 100. Going from 40 to 50 is a 25% increase, while going from 50 to 40 is a 20% decrease — the baseline differs, which is why the two answers are not the same.
Why can’t I calculate a percentage change starting from zero?
Percentage change compares the difference against the original value. When the original value is 0 there is no baseline to compare against (division by zero), so the calculator reports it as undefined instead of showing a misleading number.
Are the numbers I type uploaded anywhere?
No. The calculator runs entirely in your browser — your numbers are processed locally and are not sent to our servers.
How many decimal places are shown?
Results show up to 6 decimal places with trailing zeros removed. The exact result is rounded once at the end, so there is no hidden intermediate rounding.
How do I add or subtract a percentage from a number?
Multiply by one plus or minus the rate as a decimal. Adding 15% to 40,000 is 40,000 × 1.15 = 46,000; taking 15% off is 40,000 × 0.85 = 34,000. Doing it as two steps — find the percentage, then add or subtract — gives the same answer and is easier to check, which matters when the numbers come from someone else.
Why does adding then removing the same percentage not return the original?
Because each step uses a different base. Add 20% to 100 and you get 120; take 20% off 120 and you get 96, since the second 20% is 20% of the larger number. To reverse a 20% increase you divide by 1.2 rather than subtracting 20%. The same asymmetry is why a 50% loss needs a 100% gain to recover.
Percentage of a percentage
Multiply the decimals rather than the percentages. Thirty percent of 40% is 0.3 × 0.4 = 0.12, which is 12% — not 70% and not 1,200%. This comes up whenever a share is taken from a share, such as a commission on a margin, and writing both as decimals first prevents the mistake.