Percentage Calculator
Work out a percentage of a number, find what percent one value is of another, or measure the percentage change between two values. Pick the question, type two numbers, and the answer updates as you type.
Enter your numbers to see the result.
How the percentage formulas work
A percentage is just a fraction out of 100, so every calculation here comes down to multiplying or dividing by 100. There are three questions people ask all the time, and each has its own formula.
| Question | Formula | Example |
|---|---|---|
| What is A% of B? | A ÷ 100 × B | 15% of 200 = 30 |
| A is what percent of B? | A ÷ B × 100 | 30 is 15% of 200 |
| Percentage change from A to B | (B − A) ÷ A × 100 | 80 to 100 = +25% |
The mistake that catches almost everyone
Percentage change is not symmetric. If a price falls from 100 to 50, that is a 50% drop. But to climb back from 50 to 100 you need a 100% rise. The base number is different each time, and that is why a 20% discount followed by a 20% increase leaves you below where you started. Always ask which number the percentage is measured against.
Percent versus percentage points
If an interest rate moves from 4% to 5%, it rose by one percentage point, but it also rose by 25% in relative terms (1 ÷ 4). News headlines mix these up constantly, so check which one is meant before you quote a figure.
Where people use this calculator
Typical uses include working out sales tax, checking how much a salary rise is worth, comparing exam scores out of different totals, and measuring growth in sales or website traffic. For shopping, the discount calculator handles stacked offers and tax. For margins on what you sell, use the profit margin calculator.
[csp_calc type=”percent”]
What this percentage calculator does
This percentage calculator answers the three questions people ask most. Use X% of a number to find a discount, tip or tax amount. Use what % one number is of another to turn a score or share into a percentage. Use percentage change to measure how much a price, balance or figure has gone up or down. Choose the question from the first box and the labels update to match.
The formulas
X% of Y = Y × X ÷ 100
A is what % of B = A ÷ B × 100
Change % = (new − old) ÷ old × 100
A percentage is a fraction out of 100, so 15% means 15 out of every 100, or 0.15.
Worked examples
- Discount: a jacket costs $80 and is 25% off. 80 × 25 ÷ 100 = $20 off, so you pay $60.
- Tip: a $64 restaurant bill with an 18% tip. 64 × 18 ÷ 100 = $11.52.
- Sales tax: $120 with 8% tax. 120 × 8 ÷ 100 = $9.60, for a total of $129.60.
- What percent: 30 out of 120 is 30 ÷ 120 × 100 = 25%.
- Percentage change: a price rising from $50 to $60 is (60 − 50) ÷ 50 × 100 = 20% higher.
Why a rise then an equal fall does not cancel out
A 20% rise followed by a 20% fall does not return you to the start, because the second change is taken from a larger number. Start at 100, rise 20% to 120, then fall 20% (24) to 96. The same effect makes two 10% discounts in a row equal to 19% off, not 20%.
Common mistakes to avoid
The most frequent error is mixing up percentage points and percent. If an interest rate moves from 4% to 5%, it has risen by one percentage point, but by 25% in relative terms. Another is taking the percentage from the wrong base. Check which number your percentage is taken from before you calculate, and which value is the old one when you work out a change.
Frequently asked questions
How do I calculate a percentage of a number?
Divide the percentage by 100 and multiply by the number. For example, 15% of 200 is 15 divided by 100, which is 0.15, times 200, which equals 30.
How do I calculate percentage increase?
Subtract the old value from the new value, divide by the old value, then multiply by 100. Going from 80 to 100 gives (100 minus 80) divided by 80, which is 0.25, or a 25% increase.
What is the difference between percent and percentage points?
A percentage point is the plain arithmetic gap between two percentages. A percent change compares the gap to the starting value. Moving from 4% to 5% is one percentage point but a 25% relative increase.
How do I find the original number before a percentage change?
Divide the final number by one plus the percentage as a decimal. If a price is 120 after a 20% increase, the original was 120 divided by 1.20, which is 100.