Percentage Calculator — Free Online Percentage Calculator
Calculate percentages, percentage changes, and differences. Supports multiple operations with instant results. All calculations happen locally — nothing leaves your browser.
How do you calculate a percentage? A percentage is a number expressed as a fraction of 100, so to find a percentage of a value you multiply by the percentage and divide by 100: 25% of 200 is (25 ÷ 100) × 200 = 50. To go the other way and ask what percentage one number is of another, divide the part by the whole and multiply by 100: 45 out of 180 is (45 ÷ 180) × 100 = 25%.
How to Use the Percentage Calculator
- Pick the question you are asking — The six mode buttons map to six different questions. X% of Y finds a part, X is what% of Y finds a rate, % Change and % Difference compare two values, and Increase and Decrease apply a percentage to a starting figure.
- Enter the numbers in the right boxes — For most modes, X is the percentage and Y is the base value. For % Change and % Difference an extra box appears: put the original value in Y and the new value in Additional Value.
- Read the answer and the sentence under it — The large figure is the result; the line beneath restates the whole calculation in words, which is the quickest way to confirm you chose the mode you meant.
- Check the decimal and fraction cards — The stat cards show the same rate as a percentage and as a decimal, so you can drop the decimal straight into a spreadsheet formula without converting it yourself.
- Chain calculations when you need to — Percentages do not simply add. To apply a discount and then tax, take the result of the first calculation and use it as the base value for the second.
- Copy or share the result — Copy Result puts the figure on your clipboard, and the values and mode are stored in the page URL, so the link reopens the same calculation.
How Percentage Calculations Work
The word percent comes from per centum, Latin for "by the hundred", and that is exactly what a percentage is: a fraction with 100 as its denominator. 25% is 25/100, which is the decimal 0.25 and the fraction 1/4. Every percentage problem is a rearrangement of one relationship between a part, a whole and a rate:
part = (percent ÷ 100) × whole
Rearranged for the rate it becomes percent = (part ÷ whole) × 100, and rearranged for the total it becomes whole = part ÷ (percent ÷ 100). Those three forms answer the majority of everyday percentage questions; the calculator's first two modes cover the first two, and the third is the reverse-percentage case described below.
Percentage change measures movement relative to where a value started:
change % = ((new − old) ÷ old) × 100
The old value is the denominator, which is what makes change asymmetric. Going from 100 to 150 is a 50% increase, but going back from 150 to 100 is a 33.3% decrease, because the base changed. This is the single most common source of percentage errors in reports, and it is why a price that rises 20% and then falls 20% ends up below where it started: 100 becomes 120, then 96.
Percentage difference exists for the case where neither value is the natural baseline — two measurements of the same thing, or two competing quotes. It divides by the average of the pair instead, so the answer is the same whichever value you list first:
difference % = |a − b| ÷ ((a + b) ÷ 2) × 100
Percentages, Decimals and Fractions
| Percentage | Decimal | Fraction | Quick mental shortcut |
|---|---|---|---|
| 1% | 0.01 | 1/100 | Move the decimal point two places left |
| 5% | 0.05 | 1/20 | Take 10% and halve it |
| 10% | 0.1 | 1/10 | Move the decimal point one place left |
| 20% | 0.2 | 1/5 | Take 10% and double it |
| 25% | 0.25 | 1/4 | Halve, then halve again |
| 33.3% | 0.333 | 1/3 | Divide by 3 |
| 50% | 0.5 | 1/2 | Halve it |
| 75% | 0.75 | 3/4 | Subtract a quarter from the whole |
| 150% | 1.5 | 3/2 | The whole plus another half |
Converting between the three is mechanical: divide a percentage by 100 for the decimal, multiply a decimal by 100 for the percentage. Percentages above 100 are perfectly valid — they simply mean more than the whole, as when revenue grows to 150% of last year's figure. A percentage of a percentage works the same way, which is where percentage points matter: an interest rate moving from 4% to 5% is a rise of one percentage point but a 25% increase in the rate itself.
Common Percentage Calculations
Increase by Percentage
To increase a value by X%, multiply by (1 + X/100).
Formula: Result = Value × (1 + Percent/100)
Example: Increase 80 by 25% → 80 × 1.25 = 100
Decrease by Percentage
To decrease a value by X%, multiply by (1 - X/100).
Formula: Result = Value × (1 - Percent/100)
Example: Decrease 200 by 15% → 200 × 0.85 = 170
Percentage Difference
Compares two values without direction using their average as the base.
Formula: |A - B| / ((A + B) / 2) × 100
Example: Difference between 50 and 70 → 20 / 60 × 100 = 33.33%
Reverse Percentage
Find the original value before a percentage change was applied.
Formula: Original = Current / (1 + Change/100)
Example: After a 20% increase, value is 360 → 360 / 1.20 = 300
Examples
Example 1: Calculate a 15% Tip on $64
Use the X% of Y mode. Enter 15 for X and 64 for Y.
15% of 64 = (15 / 100) × 64 = 9.60
Example 2: Price Drops from $250 to $199.99
Use the % Change mode. Put the original price, 250, in the Y box and the new price, 199.99, in Additional Value — the old value is always the base.
((199.99 - 250) / 250) × 100 = -20.00% (20% discount)
Example 3: What Percentage is 45 of 180?
Use the X is what% of Y mode. Enter 45 for X and 180 for Y.
(45 / 180) × 100 = 25%
Frequently Asked Questions
Use the "X% of Y" mode. Enter the tip percentage (e.g. 20) for X and the bill amount for Y. The result is your tip amount.
% change compares two values over time (old vs new). % difference compares two values without direction, using the average as the base: |A-B| / ((A+B)/2) × 100.
Yes, use the result of one calculation as input for the next. For example, to apply a 10% discount then add 8% tax, first calculate the discounted price, then use that as the base for the tax calculation.
Divide rather than multiply. If a jacket costs 68 after 15% off, the sale price is 85% of the original, so the original is 68 / 0.85 = 80. In general, original = current / (1 + change/100), using a negative change for a decrease. Subtracting 15% of the sale price instead is the classic mistake and gives 78.20, which is wrong.
A percentage point is the plain arithmetic gap between two percentages; a percent change is relative. If a savings rate goes from 2% to 3%, that is a rise of one percentage point, but a 50% increase in the rate. News reports mix the two constantly, so state which you mean — the numbers can differ by an order of magnitude.
Because each percentage is taken from a different base. Starting at 100, a 20% rise gives 120, and 20% of 120 is 24, so the fall lands at 96. To undo a 20% increase you need a decrease of 16.67%. Percentage changes multiply rather than add, which is also why they never simply cancel out.
No. All six modes are computed in JavaScript in your browser, so the numbers stay on your device. One caveat: the values are written into the page URL so a link reproduces the calculation, which means a shared link carries whatever you typed. Clear the fields before sharing anything private.
Large results are abbreviated for display: thousands above 10,000 are shown with a K, millions with an M and billions with a B, and smaller numbers are rounded to four decimal places. The underlying calculation is unrounded, so re-enter a rounded figure at your own risk if you are chaining operations.
Use Cases
Tipping on a Restaurant Bill
Enter 18 and the pre-tax total in X% of Y to get the tip in cash terms before rounding up to the nearest whole amount.
Reporting Month-on-Month Growth
An analyst puts last month's figure in the base box and this month's in the additional box to state the change as a percentage rather than a raw difference.
Checking a Sale Claim
A shopper who sees "was 250, now 199.99" uses % Change to confirm the reduction is 20% and not the 30% on the sign.
Adding Tax to a Quote
A freelancer uses Increase by % to add a 21% VAT rate to a net fee, producing the gross figure that goes on the invoice.
Turning a Raw Test Score Into a Mark
A teacher converts 45 correct out of 180 into 25% with the "X is what% of Y" mode, then repeats it for each section of the paper.