Percentage Calculator
Four percentage calculations in one place — with the working shown, so you can check it or learn it.
What is X% of Y?
For working out a discount, a tip, a commission or a share of a total.
X is what percent of Y?
For a test score, a completion rate, or a share of a budget.
Percentage increase or decrease
For a price change, a salary rise, or growth between two periods.
Add or subtract a percentage
For adding sales tax, applying a discount, or a markup.
Result
The working
What this tool does
“Percentage” covers four genuinely different questions, and most people only remember how to do one or two of them reliably. This calculator handles all four, and shows the arithmetic underneath each answer rather than just handing you a number.
The four calculations
- What is X% of Y?The one you need for a discount, a tip, a commission, or a slice of a total. 20% of 250 is 50.
- X is what percent of Y?Turns two raw numbers into a rate — a test score, a conversion rate, a share of a budget. 37 out of 50 is 74%.
- Percentage increase or decreaseCompares a before and an after. Going from 80 to 100 is a 25% increase; going back from 100 to 80 is a 20% decrease — which surprises people every time.
- Add or subtract a percentageApplies a change to a number directly, for sales tax, markups and discounts. 120 plus 15% is 138.
The formulas, if you want to do it by hand
| Question | Formula | Example |
|---|---|---|
| What is X% of Y? | (X ÷ 100) × Y | 20% of 250 = 50 |
| X is what % of Y? | (X ÷ Y) × 100 | 37 of 50 = 74% |
| % change from A to B | ((B − A) ÷ A) × 100 | 80 → 100 = +25% |
| Increase Y by X% | Y × (1 + X ÷ 100) | 120 + 15% = 138 |
| Decrease Y by X% | Y × (1 − X ÷ 100) | 120 − 15% = 102 |
The mistake almost everyone makes
A percentage increase and the percentage decrease that undoes it are not the same number. If a $100 item is discounted 20% it costs $80; adding 20% back to $80 gives $96, not $100. To reverse a 20% cut you need a 25% rise.
The reason is that a percentage is always of something, and the something changes. The 20% off was 20% of $100; the 20% back on was 20% of $80. This is exactly why a stock that falls 50% needs to double — a 100% gain — just to break even, and it is worth internalising before reading any report of percentage growth.
Percent, percentage point, and basis point
These are not interchangeable, and confusing them changes the meaning entirely. If an interest rate moves from 4% to 5%, that is a rise of one percentage point — but a 25% increase in the rate itself. Both statements are true and they describe the same event. A basis point is one hundredth of a percentage point, so that same move is 100 basis points. Financial reporting relies on the distinction, so it pays to notice which one is being used.
Working out the original price from a sale price
If something cost $68 after a 15% discount, you cannot find the original by adding 15%. Divide instead: the sale price represents 85% of the original, so $68 ÷ 0.85 = $80. The same logic recovers a pre-tax amount from a total — divide by 1 plus the tax rate, never subtract the rate.
Nothing you enter is stored
The calculation runs in JavaScript on your own device. Your numbers are never sent anywhere. The share button works by writing them into the page’s URL, so only the people you send that link to will ever see them.
Frequently asked questions
How do I calculate a percentage of a number?
Divide the percentage by 100 and multiply by the number. For 20% of 250: 20 divided by 100 is 0.2, and 0.2 times 250 is 50. The 'What is X% of Y?' mode does this for you and shows the working.
How do I work out percentage increase?
Subtract the original value from the new one, divide by the original, then multiply by 100. Going from 80 to 100: (100 - 80) divided by 80 is 0.25, which is a 25% increase.
Why doesn't adding back the same percentage return the original number?
Because a percentage is always a percentage of something, and that something changes. A 20% discount on $100 gives $80; adding 20% of $80 gives $96. To undo a 20% decrease you need a 25% increase.
What is the difference between percent and percentage point?
If a rate moves from 4% to 5%, it rose by one percentage point, but by 25 percent of its own value. Both describe the same change. A basis point is one hundredth of a percentage point, so the same move is 100 basis points.
How do I find the original price before a discount?
Divide rather than add. If an item cost $68 after 15% off, that $68 is 85% of the original, so the original was 68 divided by 0.85, which is $80.
Is my data saved anywhere?
No. Everything is calculated in your browser and nothing is transmitted or stored. The share link works by putting the numbers into the page URL, which only you control.
More calculators
See the rest in Calculators — including the Tip Calculator for splitting a bill and the Mortgage Calculator for a full amortization schedule.