Percentage Calculator

A percentage calculator built as three separate calculators, for the three questions people actually ask about percentages — no mode-switching guesswork.

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Runs entirely in your browser. What you enter stays on your device — nothing is sent to a server. Verify it yourself

How do you calculate a percentage?

To find X% of a number, multiply the number by X and divide by 100 — 15% of 240 is 240 × 15 ÷ 100 = 36. To find what percentage one number is of another, divide the part by the whole and multiply by 100.

Cost: Free, no limits
Upload: None — runs on your device
Sign-up: Not required
Works offline: Yes, once loaded

How to calculate a percentage

Pick the calculation
Choose Percentage of, X is what % of Y, or Percentage change at the top.
Enter the two numbers
The labels follow the calculation — Percentage (%) and Of what number, for example, or From (original value) and To (new value).
Read the result
It updates as you type, with the calculation written out in words underneath.

Examples

15% of 24036
The everyday case: a tip, a discount, a commission.
45 is what percent of 180?25%
Used for scores, shares and completion rates.
80 → 100+25% increase
Note the asymmetry: going back from 100 to 80 is a 20% decrease, not 25%.

Key features of the Percentage Calculator

Four separate calculations: percentage of a number, what percent one number is of another, percentage increase and percentage decrease
Results update as you type — no submit button
Handles decimals and negative numbers
Shows the arithmetic, not just the answer

What it calculates

Calculations

X% of Y
X is what % of Y
Percentage change

When should you use this?

Working out a tip, a discount or a sale price.
Converting a mark out of an unusual total into a percentage.
Checking a price rise or a pay increase.
Calculating VAT or sales tax on top of a net figure.

Limitations

Percentage increase and decrease are not symmetrical. A 50% rise followed by a 50% fall does not return you to the starting value — it leaves you 25% below it. This catches people out constantly and is arithmetic, not a bug.
Adding a percentage is not the same as compounding it. Applying 10% twice gives 21%, not 20%.
Results are displayed rounded for readability; the underlying calculation uses full floating-point precision.

Troubleshooting

The increase and decrease answers disagree

They should. Percentage change is always relative to the starting number, and the two directions have different starting numbers. From 80 to 100 is +25%; from 100 to 80 is −20%.

The result has more decimal places than expected

Percentages of arbitrary numbers rarely land on round figures. The full precision is shown so you can round it yourself to whatever your context needs.

Common mistakes to avoid

Subtracting 20% to reverse a 20% addition. The correct operation is dividing by 1.2.
Averaging percentages that describe different-sized groups. A 50% success rate over 4 attempts and 50% over 400 do not average to a meaningful 50%.
Confusing "X% of Y" with "X% off Y" — the second is Y minus the first.

Pro tips

Tips for better results

Reversing
To take a percentage off, divide rather than subtract
To remove a tax or margin rather than add one, divide by 1 + the rate. Subtracting the percentage from the gross figure gives the wrong answer.
Terminology
Percentage points and percentages are not the same thing
Percentage points and percentages are different things. A rate moving from 4% to 6% is a rise of two percentage points, but a 50% increase.
Comparing
Multipliers are easier to reason about than repeated percentages
When comparing two increases, compare the multipliers rather than the percentages — 1.1 × 1.1 is easier to reason about than "10% twice".

Standards and terms behind the Percentage Calculator

The named things this tool works with, and the documents that define them.

Positional notationHow it works: Writing a number in a base — binary, octal, decimal or hexadecimal — where each column is worth a power of that base.

Also searched as: percentage increase formula, what percent of a number, percentage difference.

The three percentage questions

Almost every percentage problem is one of three shapes, and confusing them is where the arithmetic goes wrong.

X% of Y is a share of a known total: 20% of 80 is 16. Multiply the total by the percentage over 100.

X is what % of Y runs the other way — you have two numbers and want the ratio between them: 16 out of 80 is 20%. Divide the part by the whole, then multiply by 100.

Percentage change compares a before and an after: going from 80 to 96 is a 20% increase. Subtract the original from the new value, divide by the original, multiply by 100.

Why a 20% rise then a 20% fall does not return you to the start

This trips up more calculations than any other percentage mistake. Take 100, add 20% and you have 120. Now take 20% off 120 and you get 96, not 100 — because the second percentage is measured against the larger number. Percentage changes are not symmetric, and they do not add up: two consecutive 10% rises are a 21% rise, not 20%.

The same applies to discounts. A 50% discount followed by a further 20% off is not 70% off — it is 60% off, because the second reduction applies to the already-reduced price.

Percentage points versus percent

If an interest rate moves from 4% to 5%, that is a rise of onepercentage point, but a 25% increase in the rate. Both descriptions are true and they mean very different things — which is why the distinction matters whenever a change to something already measured in percent is being reported.

Privacy

The Percentage Calculator runs entirely in your browser. What you enter and the result it produces stay on your own device — nothing is sent anywhere, because nothing needs to be.

You can confirm this rather than take our word for it: open your browser’s developer tools, watch the Network tab, and use the tool. No request carries your input. It also keeps working with the connection off.

Details are in the privacy policy.

What next?

Percentages compounded over time behave differently — a repayment schedule is where that shows up most clearly.

Try the loan calculator

Percentage Calculator — questions

How do I calculate a percentage of a number?

Multiply the number by the percentage and divide by 100. For 15% of 240: 240 × 15 ÷ 100 = 36. Use the "Percentage of" tab above and it does this for you.

How do I work out a percentage increase?

Subtract the original value from the new value, divide the result by the original value, then multiply by 100. From 50 to 65: (65 − 50) ÷ 50 × 100 = 30% increase. A negative result is a decrease.

Why does adding 20% then removing 20% not give me the original number?

Because the second percentage is calculated against a different base. 100 plus 20% is 120; 20% of 120 is 24, so removing it leaves 96. To reverse a 20% increase you need to divide by 1.2, not subtract 20%.

How do I remove a percentage — for example, find the price before 20% VAT?

Divide by 1 plus the rate, not subtract the percentage. For a £120 price including 20% VAT: 120 ÷ 1.2 = £100. Subtracting 20% from 120 gives £96, which is wrong.

Is my data sent anywhere?

No. This calculator runs entirely in your browser — you can open DevTools and confirm that nothing you type is sent anywhere.

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