How to use the percentage calculator
- Pick the option that matches your question. For example, "How much is a $120 jacket with 15% off?" is the Price after discount option.
- Fill in the two fields. The labels change with the option you chose: sometimes A is a plain number and B a percent, sometimes both are ordinary values.
- Type numbers the way you normally write them:
1,250.50,1250.5and1250,5all work. The answer updates as you type, so there is no calculate button to hunt for. - Press Copy result to put a sentence such as "15% of 200: Result 30" on your clipboard, so you can paste the figure together with an explanation of what it means.
What is a percentage and how is it calculated?
A percentage is a fraction with a denominator of one hundred. When someone says "25%", they mean 25 out of every 100, which is the same as the fraction 25/100 or the decimal 0.25. Percentages are everywhere: sale prices, sales tax, restaurant tips, exam scores, interest rates, pay raises, inflation, battery levels and survey results. The reasoning never changes. Only the unknown value moves around, and that is why five slightly different formulas cover almost every everyday question.
| Question | Formula | Example |
|---|---|---|
| What is B% of A? | A × B / 100 | 15% of 200 = 200 × 15 / 100 = 30 |
| A is what percent of B? | A / B × 100 | 50 out of 200 = 50 / 200 × 100 = 25% |
| Change from A to B | (B − A) / A × 100 | 800 to 1,000 = 200 / 800 × 100 = 25% increase |
| Price after discount | Price × (1 − rate / 100) | 1,200 with 15% off = 1,200 × 0.85 = 1,020 |
| Increase A by B% | A × (1 + rate / 100) | 1,000 plus 18% = 1,000 × 1.18 = 1,180 |
The five calculations in detail
1. What is B% of A?
This is the most basic operation: finding a share of a number. Use it for the tip on a restaurant bill, the sales tax on a purchase, the commission on a deal or the deposit on a booking. Besides the main answer, the calculator also shows the number with the share added and with the share removed, so a follow-up question such as "what is the total with 18% tip?" is already answered. For example, 18% of 64.50 is 11.61, and 64.50 plus 11.61 is 76.11.
2. A is what percent of B?
Use this when you know a part and a whole and want the ratio. A student who answers 34 of 40 questions correctly scored 85%. A team that spent 3,000 of a 12,000 budget has used 25% of it. A shop where 18 of 250 visitors buy something has a 7.2% conversion rate. If the whole is zero the answer is undefined, so the tool asks you to enter a non-zero number instead of showing something misleading.
3. Percentage change from A to B
This compares an old value with a new one. A positive result is an increase and a negative result is a decrease, and the tool labels it in words so you never have to interpret a minus sign. The denominator is always the starting value. That is why going from 100 to 150 is a 50% increase, while going from 150 back to 100 is only a 33.33% decrease. The asymmetry is not an error; it is simply what happens when the base changes.
4. Price after discount
Enter the tag price and the discount rate to see what you pay and how much you save. If a store advertises "20% off, then an extra 10% at the register", do not add the rates. Work out the first price, then run the result through the calculator a second time: 1 − 0.80 × 0.90 = 0.28, so the combined saving is 28%, not 30%.
5. Increase or decrease a value by a percentage
This option applies a raise or a cut to any number: a 3% pay rise, a 5% rent increase, a 10% price cut, a 20% target reduction in energy use. Choose the direction from the drop-down. The main result is the new value, and the amount added or removed appears on the second line.
Common percentage mistakes
- Adding percentages that apply to different bases. A 50% rise followed by a 50% fall does not return you to the start: 100 becomes 150, then 75. Chain changes one step at a time.
- Using the wrong denominator. "How much did it grow?" divides by the old value. "What share is it of the total?" divides by the whole. Read the question twice before choosing a mode.
- Mixing up percent and percentage points. If an interest rate moves from 4% to 5%, it rose by one percentage point, but by 25% in relative terms. News reports blur the two all the time, and the difference can change the meaning of a headline.
- Subtracting tax the wrong way. If a price already includes 8% sales tax, multiplying by 0.92 gives the wrong pre-tax amount. Divide by 1.08 instead.
Working backwards: finding the original number
Sometimes you know the final figure and want the starting one. If a jacket costs 80 after a 20% discount, the original price is not 80 plus 20%. The sale price is 80% of the original, so divide: 80 / 0.80 = 100. The same idea works for prices that include tax or fees: divide by one plus the rate. You can check your answer with this calculator by running the original value forward through the discount option and confirming that you land on the figure you started with.
Everyday situations where this helps
Shoppers use the discount option to compare offers, such as 30% off 250 (a final price of 175) against a flat 60 off. Freelancers and small business owners use the percent-of option to add a margin or work out a deposit. Students check their grades and convert raw scores into percentages. Landlords and tenants test a proposed rent increase, and employees check what a raise really adds to a monthly pay slip. In every case the calculation is simple, but small slips in a spreadsheet or a mental estimate are common, and a quick second opinion is cheap.
For serious financial, tax or legal decisions, treat the figures here as arithmetic only. The calculator does not know your local rules, rounding conventions or fees, so confirm anything important with the seller, your accountant or the official source.
Private by design
Everything on this page is calculated by JavaScript running inside your own browser tab. The numbers you type are never uploaded, logged or stored, and the page keeps working if you disconnect from the internet after it has loaded. There is nothing to install and nothing to sign up for.
Frequently asked questions
How do I calculate a percentage of a number?
Multiply the number by the percentage and divide by 100. For example, 15% of 200 is 200 × 15 / 100 = 30. In this tool, choose "What is B% of A?", type 200 in the first box and 15 in the second.
How do I find what percent one number is of another?
Divide the part by the whole and multiply by 100. If you scored 34 out of 40, then 34 / 40 × 100 = 85%. Choose "A is what percent of B?", enter the part as A and the whole as B.
How do I calculate a percentage increase or decrease?
Subtract the old value from the new one, divide by the old value and multiply by 100. Going from 800 to 1,000 is (1,000 − 800) / 800 × 100 = 25% up. A negative result means a decrease, and the calculator spells that out in words.
Why is a 50% increase followed by a 50% decrease not back where I started?
Because each percentage applies to a different base. Start with 100, add 50% to reach 150, then take 50% of 150 away and you end at 75. To undo a 50% rise you need a one-third fall (33.33%), since the second step starts from a larger number.
How do I work out two discounts in a row?
Never add the percentages. Apply the first discount, then apply the second to the new price. With 20% off followed by 10% off, you pay 0.80 × 0.90 = 72% of the original price, which is a 28% saving in total.
What is the difference between percent and percentage points?
A percentage point is the plain arithmetic gap between two percentages, while a percent change compares them proportionally. Moving from 40% to 45% is 5 percentage points, but it is a 12.5% increase relative to the starting 40%.
Can I type numbers with commas or a decimal comma?
Yes. Both 1,250.50 and 1250.50 are read as one thousand two hundred fifty and a half. If both separators appear, the last one is treated as the decimal mark, so 1.250,50 also works. A lone comma followed by exactly three digits, as in 1,250, is read as a thousands separator.
Are my numbers sent to a server, and is the tool really free?
No data leaves your device: the arithmetic runs in your browser, and the page works offline once loaded. The tool is free with no sign-up, no daily limit and no premium version. Ads on the page are kept away from the calculator itself.
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