Percentage Calculator

How to use the Percentage Calculator

This calculator handles the four percentage tasks that come up most often.

1. Choose a modeSelect the tab that matches your question — "% of a number", "What % is X of Y", "Percentage change" or "Reverse %".
2. Enter your valuesType the numbers into the input fields. The result updates as you type, so you see the answer immediately.
3. Read the resultThe large number at the top is your answer. The line below gives the full equation for easy reference.
4. Switch modes freelySwitch between all four tabs without losing your numbers. Each panel remembers its own inputs.
5. Use the reverse modeEnter the final amount and the percentage that was applied to recover the original value before the change.

Options and variants explained

The calculator covers four distinct percentage operations. Each suits a different real-world question.

The formula explained

Percentages express a ratio per hundred, so the formula always divides the part by the whole and multiplies by one hundred. All four modes in this tool are algebraic rearrangements of the same equation.

Worked example: finding a 15% tip

A restaurant bill reads $84. You want to leave a 15% tip. Enter 15 in the percentage field and 84 in the number field. The tool returns $12.60 immediately.

Furthermore, the total to pay is $84 + $12.60 = $96.60. You can verify this in the percentage-change tab: enter 84 as original and 96.60 as new to confirm the 15% increase.

Trying the reverse mode

A jacket is priced at $119 after a 15% markup. Enter 119 as the result and 15 as the percentage applied. The tool returns $103.48 — the original wholesale price before the markup was added. Additionally, retailers use this to recover cost from a retail price.

What is a percentage?

A percentage is a way of expressing a number as a fraction of one hundred. The word comes from the Latin per centum, meaning "by the hundred". Consequently, 45% simply means 45 out of every 100.

Percentages appear in nearly every area of daily life. Discounts at shops, interest rates on loans, test scores at school and nutrition labels on food all use them. Moreover, financial media expresses growth and change almost exclusively in percentage terms.

The notation uses a percent sign (%). Furthermore, a percentage can be converted to a decimal by dividing by 100 — for example, 35% becomes 0.35. That decimal form is what calculators and spreadsheet formulas use internally.

Why percentage calculations matter

Percentages let you compare numbers of different sizes on a common scale. A $5 discount on a $10 item is much larger than a $5 discount on a $500 item, but percentages make the difference obvious: 50% versus 1%. Therefore, percentage comparisons are fair across scales.

In finance, percentage change reveals whether an investment grew or shrank and by how much. Additionally, compound interest, loan repayments and tax rates all depend on percentage arithmetic. Mistakes in these calculations can cost real money.

Tips for quick percentage maths

Finding 10% of any number is easy: move the decimal point one place left. For example, 10% of 430 is 43. Furthermore, 5% is half of 10%, so 5% of 430 is 21.5. Building larger percentages from these anchors — say 15% = 10% + 5% — keeps mental maths manageable.

To reverse a percentage, avoid the common mistake of simply subtracting the percentage. If a price rose 20%, you cannot recover the original by subtracting 20% from the new price. Instead, divide by 1.20. The reverse mode in this tool does this correctly every time.

Percentage change and percentage difference are not the same thing. Change compares a new value to an original one and has direction — positive for increase, negative for decrease. Therefore, always note which value was the starting point before computing change.

Frequently asked questions

Related tools