Percentage Calculator

About the Percentage Calculator

Percentages appear everywhere: exam results, salary raises, shop discounts, tax, interest, business growth and price inflation. This Percentage Calculator answers the six questions people ask most, each with its formula shown, so you can see how the answer was reached and repeat it on paper if you need to.

Pick the type of question, enter two numbers, and the answer updates as you type. It finds X% of a number, what percentage one number is of another, the percentage change between an old and a new value, a number increased or decreased by a percentage, and the original total when you know a part and its percentage. Students, shopkeepers, accountants, freelancers and anyone checking a bill or a payslip can use it without signing up.

What is a percentage?

A percentage is a way of writing a fraction out of 100. “Per cent” means “per hundred”, so 25% means 25 out of every 100, or 0.25. Percentages make it easy to compare amounts of different sizes: 45 out of 60 and 60 out of 80 are both 75%.

Every percentage problem involves three quantities: the whole (base), the part, and the rate as a percentage. They are linked by one formula: part = whole × rate ÷ 100. Rearranging that formula gives the other questions. Rate = part ÷ whole × 100, and whole = part ÷ rate × 100. Percentage change is a special case where the base is the starting value: (new − old) ÷ old × 100.

It also helps to know the difference between percent and percentage points. If an interest rate rises from 10% to 12%, it has gone up by 2 percentage points, which is a 20% increase in the rate itself.

How to use the Percentage Calculator

1. Choose the calculation type at the top: X% of Y, X is what % of Y, % change, Increase by %, Decrease by % or Find the total.
2. Read the sentence under the buttons; it shows what Value A and Value B mean for that type.
3. Enter Value A and Value B. Decimals and negative numbers are accepted.
4. Read the large result and the formula or working shown under it.
5. Use Copy result to copy the answer, or Reset to return to the example values.

If a calculation is impossible, for example a percentage change from a starting value of zero, the tool explains why instead of showing a misleading number.

Key features and benefits

• Six calculation types. Covers almost every everyday percentage question in one place
• Formula shown. Each answer includes the working, which is useful for homework and for checking invoices
• Live results. Answers update on every keystroke, with no button to press
• Correct handling of negatives. Percentage change uses the absolute value of the starting number, so changes from negative values have the correct sign
• Clear error messages. Division by zero and other impossible inputs are explained
• Precise. Results are shown with up to six decimal places and no rounding surprises
• Private and offline. All calculations run in your browser

Practical examples

Marks as a percentage

You scored 72 out of 90. Choose “X is what % of Y”, enter 72 and 90: (72 ÷ 90) × 100 = 80%.

Discount on a price

A Rs 2,400 shirt is 15% off. “X% of Y” with 15 and 2,400 gives Rs 360 off. Or use “Decrease by %” with 2,400 and 15 to get the sale price directly: Rs 2,040.

Price change

A litre of milk went from Rs 200 to Rs 220. “% change” with 200 and 220 gives +10%. If it later falls back to 200, the change from 220 is −9.09%, not −10%, because the base is now 220.

Removing tax from a total

A bill of Rs 1,180 includes 18% tax. Taking 18% off 1,180 gives 967.60, which is wrong. The price before tax is the total that 1,180 is 118% of. Use “Find the total” with 1,180 and 118 to get Rs 1,000.

Two discounts in a row

A 20% discount followed by an extra 10% is not 30% off. Rs 1,000 becomes 800, then 720: a total discount of 28%.

Markup versus profit margin

A shopkeeper buys an item for Rs 800 and sells it for Rs 1,000. The profit is Rs 200. As a markup on cost, use “X is what % of Y” with 200 and 800: 25%. As a profit margin on the selling price, use 200 and 1,000: 20%. Both are correct, but they answer different questions, so always say which one you mean when quoting prices to a supplier or customer.

Common use cases

• Students convert marks to percentages and check exam results and grade boundaries.
• Shoppers work out sale prices, compare discounts and check whether a “deal” is real.
• Business owners calculate markups, margins, sales growth and target achievement.
• Employees check salary raises, bonuses and deductions.
• Analysts and journalists describe changes in prices, population or data correctly.

Accuracy, limitations and privacy

The calculator uses standard formulas: part = A × B ÷ 100; rate = A ÷ B × 100; change = (B − A) ÷ |A| × 100; increase = A × (1 + B ÷ 100); decrease = A × (1 − B ÷ 100); total = A ÷ (B ÷ 100). Results are calculated with your browser’s double-precision arithmetic and shown with up to six decimal places, so very long decimal answers are rounded for display.

Nothing you type is stored or sent anywhere; the page works offline once loaded.

• Percentage change is undefined when the starting value is zero, so the tool shows an error instead of an answer.
• Display rounding means very small differences may not be visible; copy the result if you need it in a spreadsheet.
• The calculator does not know about compounding; for interest over several periods, use the compound interest calculator.

Tips and best practices

• Always ask “percentage of what?” — most percentage mistakes come from using the wrong base.
• To remove a percentage that was added, divide by (1 + rate ÷ 100) rather than subtracting the percentage.
• Chain discounts by multiplying: 20% then 10% off is 0.8 × 0.9 = 0.72 of the original price.
• When reporting changes in rates, say “percentage points” for differences and “percent” for relative changes.
• Round only at the end of a calculation to avoid small errors adding up.

Related tools and next steps

For shop prices with one or more discounts, try the Discount Calculator; for buying and selling prices, the Profit and Loss Calculator. Add or remove sales tax with the GST Calculator or VAT Calculator. Students in Pakistan can total several subjects with the marks percentage calculator, and investors can see growth over time with the Compound Interest Calculator.