Percentage Calculator

Percentages turn up in tips, discounts, exam scores, tax add-ons, and growth reports—yet the three common question types trip people up. This calculator handles “what is X% of Y,” “what percent is X of Y,” and percent change between two values in one place. Enter the numbers for the mode you need and read the result as you type. Use it when you want a trusted check against mental math or a spreadsheet formula. Everything runs locally in your browser so your figures stay private.

X% of Y

Result: 30

X is what percent of Y

Result: 25%

Percent change

Result: 25%

Informational only; verify critical results independently.

How to use

  1. Pick the mode that matches your question: X% of Y, what percent X is of Y, or percent change from an old value to a new value.
  2. For “percent of,” enter the percentage and the base amount (for example 18 and 85.00 for an 18% tip on $85).
  3. For “what percent,” enter the part and the whole so the tool can express the part as a share of the whole.
  4. For percent change, enter the starting value first, then the ending value; a rise shows positive change and a drop shows negative.
  5. Watch units: keep money in the same currency, scores out of the same maximum, and avoid mixing “percentage points” with relative percent unless you intend to.
  6. If results look off, check zeros and decimals—0.5% of 200 is not the same as 50% of 200, and a baseline of zero makes relative change undefined.
  7. Round for the audience: banks and receipts often use two decimal places for currency even when the underlying math is more precise.
  8. Cross-check multi-step stories (tax then tip, or discount then fee) by running each step separately and feeding the intermediate result into the next.
  9. Use percent change when comparing a metric over time, and part–whole when you need a share of one period’s total.
  10. Save or jot the inputs with the result so you can reproduce the same calculation later for a report or budget note.

Examples

  • 15% of 240 = 36 (classic tip or discount amount on a $240 base).
  • What percent is 45 of 200? 45 ÷ 200 × 100 = 22.5%.
  • Percent change from 80 to 100 = (100 − 80) ÷ 80 × 100 = 25% increase.
  • 20% of a $65.00 bill = $13.00 tip; total with tip = $78.00.
  • Saved $12 on an $80 item → 12 ÷ 80 × 100 = 15% off.
  • Increase 250 by 6%: 250 × 1.06 = 265.
  • Decrease 400 by 12%: 400 × 0.88 = 352.
  • Test score: 57 correct out of 60 → 57 ÷ 60 × 100 = 95%.
  • VAT-style add-on: 20% of a $150 net price = $30 tax; gross = $180.
  • Recovery after a drop: fall from 100 to 80 (−20%), then rise to 100 is a +25% change from the new base of 80.

FAQ

How do I find X% of Y?
Multiply Y by X divided by 100. In decimal form, convert the percent to a fraction of one (15% → 0.15) and multiply. Example: 15% of 240 = 240 × 0.15 = 36.
How do I find what percent X is of Y?
Divide the part by the whole, then multiply by 100. Example: 45 of 200 is 45 ÷ 200 × 100 = 22.5%. The whole must not be zero.
What is the difference between percentage points and relative percent?
Moving from 10% to 12% is a change of 2 percentage points. Relative to the old rate, the increase is (12 − 10) ÷ 10 = 20%. Always say which meaning you intend in reports and policy discussions.
Why is percent change undefined when the old value is zero?
Relative change divides by the baseline. Dividing by zero is undefined, so there is no finite percent change from a true zero start. Use absolute difference instead, or choose a non-zero baseline if one applies.
Can I use this for sales tax or VAT math?
Yes for the arithmetic. To add tax, compute tax% of the net and add it. To reverse a tax-inclusive price, divide by (1 + rate) when the rate is known. Confirm statutory rules for your jurisdiction separately.
Does the calculator round the way my bank or POS does?
We show precise intermediate math and readable display rounding. Card networks, banks, and cash registers may apply half-up, banker’s rounding, or truncate to cents differently. Treat currency results as estimates until the receipt confirms.
How do successive percentage changes work?
Apply them multiplicatively. A 10% rise then a 10% fall does not return to the start: 100 × 1.10 × 0.90 = 99. Work each step on the current base rather than adding or subtracting percentages.
When should I use this tool instead of a dedicated tip or discount calculator?
Use this when you need flexible percent-of, part–whole, or change math. Tip and discount tools add convenience fields (splits, sale-price breakdowns) for those workflows, but the core percentage rules are the same.
Can percentages exceed 100%?
Yes. A value can be more than 100% of another when the part exceeds the whole (for example 150 is 150% of 100), and growth can exceed 100% when the new value more than doubles the old one.
How precise should I leave answers for homework or exams?
Follow the teacher’s rounding rules. Often leave intermediate work unrounded and round only the final answer to the requested decimals or significant figures.
Do negative bases or negative percents work?
The formulas still apply algebraically, but interpretation depends on context. Negative growth is a decrease; a negative base (such as a loss figure) needs a carefully worded explanation so readers are not misled.
Is my data sent to a server?
No. Calculations run in your browser. We do not store the numbers you type for this tool.

Formula / Method

Percent of: result = Y × (X ÷ 100). Part as percent of whole: (part ÷ whole) × 100. Percent change: ((new − old) ÷ old) × 100. Increase by P%: multiply by (1 + P/100); decrease by P%: multiply by (1 − P/100).

Assumptions & Limitations

Results depend entirely on the numbers and mode you choose. The tool does not apply tax law, bank rounding policies, or compounding schedules beyond a single percent operation. Percent change from a zero baseline is undefined. This is arithmetic help, not financial advice.

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Last updated: 2026-07-13

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