Percentage calculator with steps
Work out X% of Y, what percent one number is of another, percentage increase or decrease, and add or subtract a percentage — with steps.
- Runs in your browser
- Nothing you enter is sent
- Free, no account
Answer
As a fraction of the whole
0.15
decimal multiplier
Remaining after taking it out
204
85% of 240
Number plus this percent
276
240 × 1.15
Step-by-step working
Write the percentage as a decimal by dividing by 100.
15% = 15 ÷ 100 = 0.15Multiply that decimal by the number.
0.15 × 240 = 36Answer.
15% of 240 = 36The same answer comes from (percent × number) ÷ 100 — the order of the two operations does not matter.
Formula used: result = (X ÷ 100) × Y
How to use the percentage calculator
Percentage questions come in four shapes, and mixing them up is the single most common source of arithmetic mistakes. Pick the tab that matches the sentence you are trying to answer:
- X% of Y — “what is 15% of 240?”. Use this for tips, sales tax, commission and any share of a known total.
- X is what % of Y — “36 out of 240 is what percent?”. Use this for test scores, conversion rates and market share.
- % increase or decrease — “sales went from 80 to 100, by what percent?”. Use this whenever you are comparing a new figure against an earlier one.
- X plus or minus Y% — “add 20% VAT to 250” or “take 30% off 89.99”. Use this to apply a percentage rather than measure one.
Every tab updates as you type and shows the full working underneath, including the decimal multiplier it used. Copy the steps with one button if you need to paste them into homework or a spreadsheet note.
The four formulas
| Question | Formula | Worked example |
|---|---|---|
| What is X% of Y? | (X ÷ 100) × Y | 15% of 240 = 0.15 × 240 = 36 |
| X is what percent of Y? | (X ÷ Y) × 100 | 36 of 240 = 0.15 × 100 = 15% |
| Percentage change old → new | (new − old) ÷ |old| × 100 | 80 → 100 = 20 ÷ 80 = +25% |
| Add or subtract a percentage | X × (1 ± Y ÷ 100) | 250 + 20% = 250 × 1.2 = 300 |
Percentage traps worth knowing
Percentages do not add up
A 10% rise followed by another 10% rise is not a 20% rise. The two multipliers compound: 1.10 × 1.10 = 1.21, so the total is a 21% increase. The same logic explains why a 50% discount followed by a further 20% off is a 60% discount, not 70%: 0.5 × 0.8 = 0.4, and you pay 40% of the original.
Going up and back down does not return you to the start
Rise 25% from 80 and you get 100. Fall 25% from 100 and you get 75, not 80. The rise was measured against 80 and the fall against 100 — different bases, different sized steps. To undo a p% increase you need a decrease of p ÷ (100 + p) × 100 percent.
Percentage points are not percent
If an interest rate moves from 4% to 5%, that is a rise of one percentage point but a 25% increase in the rate itself. News reports mix these up constantly; the “% increase” tab always reports the relative change, which is the second reading.
Percentage change versus percentage difference
Percentage change is directional and uses the starting value as its base. Percentage difference is symmetric and uses the average of the two values, so comparing A with B gives the same answer as comparing B with A. The change tab shows both figures so you can quote the right one.
Quick mental shortcuts
- 10% — move the decimal point one place left. 10% of 63 is 6.3.
- 5% — half of 10%. 5% of 63 is 3.15.
- 1% — move the point two places left. 1% of 63 is 0.63.
- 15% tip — 10% plus half of it again. 10% of 48 is 4.80, plus 2.40, gives 7.20.
- Reversibility — X% of Y always equals Y% of X. 18% of 50 is awkward; 50% of 18 is obviously 9.
Accuracy and privacy
Calculations run in double-precision floating point, the same arithmetic every spreadsheet uses, and results are shown to up to ten decimal places with trailing zeros trimmed. Nothing you type is transmitted anywhere: the calculator is JavaScript that runs inside your browser tab, so it keeps working with the network switched off.
Questions
How do I calculate a percentage of a number?
Divide the percentage by 100 and multiply by the number. 15% of 240 is 0.15 × 240 = 36. The "X% of Y" tab does exactly that and shows both lines of working.
What is the difference between percentage change and percentage difference?
Percentage change compares a new value against a specific starting value, so it has a direction. Percentage difference compares two values against their average, so the order does not matter.
Why is a 50% rise followed by a 50% fall not back to the start?
Each percentage is taken from a different base. 100 rises to 150, then 50% of 150 is 75, so you land on 75. The tool shows the base used at every step so the asymmetry is visible.
Can I use decimals and negative numbers?
Yes. Any real number works, including negatives and decimals. Percentage change from a negative starting value is reported against the absolute value of that base, which is the usual convention.
Does anything I type get uploaded?
No. The whole calculator is JavaScript running in your browser tab. Nothing is sent anywhere, and the page works offline once loaded.