Percentage calculator online

How to use the percentage calculator

1. Choose the calculation you need: X% of Y, X is what % of Y, or increase/decrease Y by X%.
2. Enter X and Y.
3. Read the result, which updates as you type.
4. Switch calculation modes to answer a different percentage question with the same numbers.

"X% of Y" answers questions like "what is 20% of 150?". "X is what % of Y" answers questions like "45 is what percent of 300?". The increase/decrease modes answer questions like "increase 80 by 15%".

The four percentage calculations, explained

X% of Y multiplies Y by X/100, answering "what is X percent of Y?" (a tip, a commission, a portion of a total). X is what % of Y divides X by Y and multiplies by 100, answering "what share does X represent of Y?" (a test score out of a total, a budget line as a share of spending). Increase/decrease Y by X% adds or subtracts X percent of Y from Y itself, answering "what does Y become after a percentage change?" (a price increase, a pay raise, a markdown).

Best practices

• Match the calculation mode to the actual question. "20% off $100" is a decrease calculation, not "X% of Y" — the wording matters for which mode gives the right answer.
• Double-check which number is X and which is Y for the "is what %" mode, since swapping them gives a very different (and wrong) answer.
• Use the discount calculator directly for shopping discounts, since it's purpose-built with "you save" framing rather than requiring you to interpret a generic percentage result.
• Round only your final answer, not intermediate values, if you're doing a multi-step calculation by hand alongside this tool, to avoid compounding rounding errors.

Common mistakes to avoid

• Confusing "increase by X%" with "X% of the new total." Increasing 100 by 20% gives 120, not the same as finding what number, when increased by 20%, equals 100 (that would be roughly 83.3).
• Chaining percentage changes incorrectly. A 20% increase followed by a 20% decrease does not return you to the original number; the second decrease applies to the already-increased value.
• Treating percentage points and percent the same way. Going from 10% to 15% is a 5 percentage point increase but a 50% relative increase; be clear about which one your context needs.

Real-world use cases

• Calculating a tip at a restaurant (X% of the bill).
• Working out a test or survey score as a percentage of the total possible.
• Estimating a price after a raise or markdown (increase/decrease mode).
• Checking a commission or bonus calculation that's supposed to be a percentage of a base figure.
• Comparing two survey or poll results reported as raw counts by converting each to a percentage of its own total first.

Worked example: comparing all four modes with the same numbers

Using X=20 and Y=100 across all four modes shows how differently each one answers a "percentage question":

Supported formats

X and Y accept positive or negative numbers, with decimal values (like 12.5) supported to any precision your browser's number input allows. There is no fixed upper limit on the values you can enter, though extremely large numbers may display in scientific notation depending on your browser.

Why percentage questions are so often phrased ambiguously

Everyday language about percentages is genuinely ambiguous in ways that matter for the math. "Sales went up by 20%, then down by 20%" sounds like it should net out to zero, but it doesn't, because each change is relative to a different starting point. "This item is 20% cheaper than that one" and "that item is 20% more expensive than this one" also describe different ratios, not the same relationship viewed from two sides — a common source of confusion in comparison shopping and reporting. When a percentage question feels ambiguous, it usually helps to identify explicitly which number is the "before" value and which is the "after" value before picking a calculation mode.

Limitations

This calculator performs the four percentage operations listed above only; it does not chain multiple percentage changes in sequence or calculate compound percentage change over time (for that, see the SIP calculator or EMI calculator, which apply compounding over a schedule).

Privacy

All calculation happens locally in your browser as you type. Nothing is sent to a server. See the privacy policy for the site's full data handling approach.

Troubleshooting

• If the result looks wrong, double-check you picked the calculation mode that actually matches your question.
• If you need a shopping discount specifically, try the discount calculator for clearer "you save" framing.
• If Y is zero in "X is what % of Y" mode, the result is undefined (division by zero); enter a non-zero base value.

Conclusion

Use this calculator for quick percentage math in any of its four common forms. For a shopping-specific discount calculation, see the discount calculator; for GST-inclusive/exclusive amounts, see the GST calculator.