Percentage calculator.
Made simple.

A percentage is a comparison with 100.

Percent means “per hundred.” Saying 25% is another way to say 25 out of 100, 0.25, or one quarter. The scale makes it easier to compare quantities with different totals: 18 correct answers out of 20 and 45 out of 50 both represent 90%.

Our percentage calculator puts the common questions in plain language. You can find a portion of a total, turn a fraction into a percentage, recover the whole from a known share, or compare two values. The answer matters, but understanding the denominator matters just as much: it tells you what your percentage is measured against.

How to use this percentage calculator

1. Choose your question. “% of a number” finds an amount; “What percent?” finds a rate. Use percentage change when you have an original and a new value.
2. Enter your numbers. Type 15 for 15%, rather than 0.15. Decimals are welcome. Leave currency symbols and the percent sign out of number fields.
3. Select Calculate. Read the result and the substituted formula beside it.
4. Check the context. A result of 30 could mean dollars, students or units. The percentage calculator does not infer a currency or real-world meaning.

Use “Try an example” to see a completed calculation, Clear to start again, and the decimal-place setting when you need a more detailed display. Copy result lets you carry the answer and working into your notes.

The percentage formula cheat sheet

Most percentage problems involve a part, a whole and a rate. If you know two of them, you can usually find the third. Let p represent a percentage such as 15, rather than its decimal form 0.15.

Work through three familiar examples.

1. Find a percentage of a number

Suppose a group has 240 members and 35% attend an event. Divide 35 by 100 to get 0.35, then multiply by 240. The expected count is 84 members. This is the “% of a number” question: you already know the rate and the total.

2. Calculate an exam percentage

A student earns 68 marks out of 80. Divide the earned marks by the available marks, then multiply by 100. The result is 85%. This shows the score as a percentage; it does not determine a letter grade, because grading policies differ.

3. Measure a change over time

A weekly order count rises from 120 to 150. The increase is 30 orders, measured against the original 120. Divide 30 by 120 and multiply by 100 to get 25%. Reversing the direction gives a different rate: a drop from 150 to 120 is 20%.

Use percentages in everyday decisions.

Shopping, discounts and original prices

For 30% off a price of 90, the saving is 27 and the sale price is 63 before tax. If all you know is that a sale price of 63 follows a 30% discount, divide by 0.70 to recover the original 90. Adding 30% to 63 would give 81.90, which is not the original price. Use the discount calculator or reverse percentage calculator for those separate questions.

Tips and simple tax estimates

A 15% tip on a bill of 48 is 7.20. Adding that amount gives 55.20 before any other charges. For a simple tax estimate with the percentage calculator, multiply the taxable amount by the stated tax rate and add it to the base. Actual rules can depend on location, taxable items and rounding, so this is arithmetic rather than a tax determination.

Progress, goals and completion

Use the percentage calculator to check completion. Use the percentage calculator to check completion. If you finish 36 of 48 tasks, your completion rate is 75%. If your target later changes to 60 tasks, the same completed count represents 60%. Keep the whole consistent when comparing progress reports; otherwise a percentage can change even when the completed work has not.

Rates in reports and surveys

A response rate moving from 40% to 50% rises by 10 percentage points and by 25% relative to the original rate. Both descriptions are valid, but they answer different questions. The percentage points calculator helps you report the absolute movement without confusing it with relative growth.

Small mistakes that change the answer

• Dividing by the wrong total. Use the whole for a share, the original value for a change, and the mean for a symmetric difference.
• Entering a decimal as a percentage. In a percentage field, 0.15 means 0.15%, not 15%.
• Adding successive discounts. A 20% reduction followed by 10% off the reduced price is a 28% total reduction, not 30%.
• Rounding too early. In the percentage calculator, keep intermediate values precise, then round the final answer to match the context.
• Assuming the result must be below 100%. 150 is 150% of 100. Rates above 100% can be meaningful.

What happens with zero and negative numbers?

Zero percent of a number is zero. Dividing by a zero whole is undefined, so the percentage calculator asks you to change the input. Percentage change here requires a positive starting value: relative movement from zero has no finite percentage, while negative baselines can produce misleading interpretations. Basic percentage calculations can still accept signed values where the arithmetic is well-defined.

The percentage difference tool uses nonnegative values and the arithmetic mean. Two zero values have a zero mean, so that calculation is undefined under this formula. Comparing zero with a positive value gives a symmetric difference of 200%.

Precision and limitations

The percentage calculator uses JavaScript floating-point arithmetic and display up to the selected number of decimal places. Very small or very large numbers can be affected by machine precision. The tools support learning and everyday calculations; verify consequential results independently and use appropriate specialist software where exact decimal accounting is required.

Frequently asked questions

Make the question clear. The maths follows.

A reliable percentage calculator answer starts with knowing what the percentage describes. Identify the part and whole, or choose the correct reference for a comparison, before entering the values. Then use the displayed formula to check that the operation matches the question you intended to ask.

This percentage calculator brings the common operations together, while the dedicated tools and guides explain the differences in more detail. Whether you are checking a sale, reviewing a score or describing a change, keep the units and baseline in view. Use the answer to support your decision rather than treating an unexplained number as the whole story.

Further learning: Maths Is Fun: percentages. Educational reference reviewed October 26, 2026.