Percentage Calculator

What does this percentage calculator do?

It answers seven different percentage questions, because "percentage" is one word covering several separate calculations that people constantly mix up.

• What is X% of Y for a portion: a tip, a commission, a share of a budget.
• X is what % of Y for turning a fraction into a rate: a test score, a conversion rate.
• X is Y% of what for working backwards to the original number.
• Increase or decrease for the percent change between a before and an after.
• Add or subtract % for a price with tax added or a discount taken off, in one step.
• Percentage difference for comparing two values when neither one is the baseline.
• Percentage points for the gap between two rates, which is not the same as percent change.

Every answer shows the working underneath, so you can check the result instead of trusting it. Everything runs in your browser, and nothing you type is uploaded or stored.

How do I use it?

Pick the tab that matches your question. The sentence under the tabs restates it in full, and the field labels change with it, so it is always clear which number goes where.

Type the two numbers. The result updates as you type. There is no calculate button and no page reload.

Read the working. Under the big figure you get the formula with your numbers substituted in, like 15 ÷ 100 × 80 = 12. That line is there so you can redo the calculation by hand or explain it to someone else.

Copy the answer with the button, if you need it somewhere else.

How do I find the original price before a discount?

Work out what percentage of the original you actually paid, then use the reverse mode.

A 20% discount means you paid 80% of the original. So if the sale price is $150, the question is "150 is 80% of what", and the answer is $187.50. A 25% increase means the new figure is 125% of the old one, so $5,500 after a 25% raise means the salary before it was $4,400.

This is the calculation most percentage tools leave out, and it is the one people actually need when they are staring at a receipt.

What is the difference between percentage points and percent?

Going from 40% to 44% is a rise of 4 percentage points, and at the same time a 10% increase. Both statements are true and they describe the same move.

Percentage points are the plain subtraction between two rates: 44 minus 40. Percent change divides that gap by where you started: 4 divided by 40. Whenever the thing being measured is already a percentage, an interest rate, an unemployment figure, a conversion rate, a tax band, these two numbers separate and the difference between them can be enormous.

A rate moving from 2% to 3% is 1 percentage point and a 50% increase. Headline writers pick whichever sounds better. The last mode on this calculator shows both numbers side by side so you can see which one is being used on you.

When should I use percentage difference instead of percent change?

Use percent change when one value is clearly the starting point: last month's revenue, the original price, the previous reading. It divides by that starting value, so swapping the two numbers gives a different answer.

Use percentage difference when neither value is the baseline: two suppliers' quotes, two lab measurements, two branches in the same month. It divides by the average of the two, so the order does not matter and you get a single symmetric number.

Comparing 50 and 65: the change from 50 to 65 is 30%, the change from 65 to 50 is 23.08%, and the percentage difference between them is 26.09% whichever way round you type them.

Why is a 50% rise then a 50% fall not back where you started?

Because each percentage is measured against a different number.

Start at 100 and add 50%: you get 150. Now take 50% off 150 and you get 75, not 100. The rise was 50% of 100, the fall was 50% of 150, and those are different amounts. To undo a 50% rise you need a 33.3% fall.

This is the same reason a stock that drops 50% needs to gain 100% to recover, and it is the single most common percentage mistake in everyday reasoning.

What this calculator does not do

Being clear about the edges matters more than pretending to cover everything.

• It does not calculate interest over time. Compound interest, loan repayments and annual growth rates all involve a percentage applied repeatedly across periods. That is a different formula, and treating it as a single percentage will give you a wrong number.
• It does not know your tax rate. The add-and-subtract mode applies whatever percentage you type. Sales tax, VAT and service charges vary by country, state and product, and this tool has no way of knowing which applies to you.
• It does not convert markup to margin. They are different percentages of different bases: a 50% markup on cost is a 33.3% margin on the selling price. Entering one where you meant the other is a common pricing error and this calculator cannot tell which you intended.
• It does not round to a currency. Results keep up to six decimal places. If you are working with money, round the final answer yourself to the precision your situation requires.
• It does not keep a history. Nothing is stored between sessions. Copy anything you want to keep before you leave the page.

Is my data private?

Yes. The calculator is fully client-side, running plain arithmetic in JavaScript on your device. The numbers you enter never leave your browser, are never logged, and clear when you close the tab. Once the page has loaded it keeps working with no connection at all.