Percentage Calculator
Three percentage calculations in one tool. Pick the mode, type two numbers, and the answer appears as you go.
Results are estimates. Solvemis accepts no responsibility for the results obtained or for how they are used.
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How it works
How to use it
- Pick what you want to work out: X% of a number, what percent one number is of another, or the change between two values.
- Type the two numbers. Thousands separators are fine: 30,000 is read as thirty thousand.
- The answer appears as you type. For changes, the sign tells you whether it is an increase (+) or a decrease (−).
How it is calculated
A percent is a fraction of 100: 15% is 0.15. X% of Y is X ÷ 100 × Y; what percent X is of Y is X ÷ Y × 100; and the change from X to Y is always divided by the starting value, never the ending one.
Percent change = (Y − X) ÷ |X| × 100
Sources
- NIST Guide to the SI, Chapter 7, section 7.10.2 (Percent) — National Institute of Standards and Technology (NIST)
About this calculator
The three calculations it covers
Almost every percentage question falls into one of three shapes, and this tool handles all three in one place.
What is X% of Y
The everyday one: discounts, tips, sales tax, commission. Divide the percentage by 100 and multiply by the amount.
21% of $450 = (21 ÷ 100) × 450 = $94.50
X is what percent of Y
Use this to express a part against a whole — what share of your income a bill takes, how much of a test you got right. Divide the part by the total, then multiply by 100.
45 correct out of 60 questions = (45 ÷ 60) × 100 = 75%
Percentage change from X to Y
Compares two points in time: a price rise, a bill over two quarters, a metric week on week. Subtract the starting value from the ending value, divide by the starting value, multiply by 100.
From $80 to $92 = ((92 − 80) ÷ 80) × 100 = +15%
A negative result means a decrease. The division is always by the starting value, never the ending one — that is the single most common mistake here, and it changes the answer.
Three errors that cost real money
Chaining percentages as if they add up. Two successive 20% discounts are not 40%. On $100, the first leaves $80 and the second takes off $16, not $20 — the final price is $64, a real discount of 36%. Chained percentages multiply; they do not add.
Subtracting a percentage to undo it. To get the pre-tax figure from a price that includes 21% tax, do not subtract 21% — divide by 1.21. Subtracting 21% from $121 gives $95.59, while the true base is $100. The percentage was applied to the base, not to the total.
Confusing percentage points with percent. This is the favourite trick of headlines. Unemployment moving from 4% to 6% is a rise of two percentage points, and also an increase of 50%. Both are accurate descriptions of the same event; using one where the other belongs inflates or deflates the story at will.
Shortcuts worth memorizing
- 10% is the decimal point moved one place left. 10% of 340 is 34.
- 5% is half of 10%. 5% of 340 is 17.
- 1% is the decimal point moved two places. 1% of 340 is 3.4.
- Those three build most others: 15% is 10% + 5%, and 20% is 10% twice.
- Percentages commute: 8% of 50 equals 50% of 8. Both are 4. When a calculation feels awkward, flip it around and it usually solves itself.
Frequently asked questions
How do you find X% of a number?
Divide the percentage by 100 and multiply by the number. 15% of 200 is (15 ÷ 100) × 200 = 30.
If a price rises 20% then falls 20%, is it back where it started?
No. A $100 item rising 20% becomes $120, and 20% off $120 is $24, leaving $96. Each percentage applies to a different base.
What is the difference between a percentage point and a percent?
If a rate moves from 2% to 3%, that is a rise of one percentage point — but it is also a 50% increase on the previous value. Mixing the two changes the apparent size of the number completely.
Updated September 28, 2026
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