Percentage Calculator
Percent of a number, what percent, percentage change, reverse percentages and stacked discounts.
How to use
- Pick the section that matches your question. Every section already holds an example, so you can see how it works before typing anything.
- Type your own numbers. Decimals work with a point or a comma, and a trailing % sign is ignored.
- Read the result right below the inputs. The grey line under it shows the formula with your numbers, so you can check it or copy the steps into homework or a spreadsheet.
- For shopping, use the discount calculator at the bottom. Add a second discount when a sale price gets an extra coupon or a "further 10% off at checkout".
Six percentage questions, one page
Most percentage problems are one of a handful of shapes, and this page puts each one in its own section so you never have to rearrange a formula. The answer updates as you type, and the line under each result spells out the arithmetic with your own numbers. Numbers are shown with US formatting (1,234.5), and you can type them with or without thousands separators.
- What is X% of Y? The tip, the tax or the commission. 18% of a $64 restaurant bill is 64 × 18 ÷ 100 = $11.52.
- X is what percent of Y? Test scores, budget shares, survey results. 42 votes out of 280 is 15%.
- Percentage change from A to B. Price rises, salary raises, stock moves, weight loss. The result carries a sign: +25% is an increase, −12% a decrease.
- Add or subtract a percentage. A 3% raise on $58,000, or a price 15% lower. Both directions are shown side by side.
- Find the original value. Work backwards from a sale price or a price with tax included.
- Discount calculator. Price, one or two discounts, the final price and what you save.
Why percentages don’t simply add up
A percentage is always a share of some base, and the base changes as you go. A stock that falls 50% and then rises 50% ends at 75% of where it started, because the rise is measured from the lower price. In the same way, a 20% markdown followed by an extra 10% at the register multiplies the price by 0.8 and then by 0.9, which is 0.72: a total discount of 28%. Stores sometimes advertise “up to 30% off” for exactly this combination. The discount calculator shows the true total and the amount you keep in your pocket.
Going backwards trips people up for the same reason. If a jacket costs $48 after 20% off, the original price is not $48 plus 20% ($57.60) but $48 ÷ 0.8 = $60. The reverse section shows both cases: the price before a discount and the value before an increase such as sales tax or a markup.
Percentage change versus percentage points
When the old value is a percentage itself, such as an interest rate or an exam pass rate, there are two ways to describe a change. From 4% to 5% is one percentage point, and also a 25% relative increase. News reports mix the two, so it helps to check which one you are looking at. For growth that repeats every year, such as savings earning interest on interest, a single percentage change isn’t enough: the compound interest calculator runs the numbers year by year. For grade averages weighted by credits, try the GPA calculator.
Accuracy
Results are rounded to two decimal places for display, which suits money and most everyday questions. Very small results keep three significant digits so they don’t show as zero. Everything runs in your browser; nothing you type is sent anywhere.
Frequently asked questions
How do I calculate a percentage of a number?
Multiply the number by the percentage and divide by 100. 20% of 150 is 150 × 20 ÷ 100 = 30. In your head, find 10% by moving the decimal point one place left (15) and double it.
How do I work out what percent one number is of another?
Divide the part by the total and multiply by 100. If you got 30 questions right out of 120, that is 30 ÷ 120 × 100 = 25%.
How is percentage change calculated?
Subtract the old value from the new one, divide by the old value and multiply by 100. Rent going from $1,600 to $1,720 is (1,720 − 1,600) ÷ 1,600 × 100 = +7.5%. A minus sign means a decrease.
Is 20% off and then 10% off the same as 30% off?
No. The second discount is taken from the already reduced price, so together they make 28% off, not 30%. The discount calculator shows this total discount next to the final price.
How do I find the original price before a discount or tax?
Divide the price you paid by what remained as a fraction. After 20% off you paid 80%, so $48 ÷ 0.8 = $60. A price of $107 including 7% sales tax was $107 ÷ 1.07 = $100 before tax. Taking 20% off $48 gives $38.40, not $60, which is a common mistake.
Why does it say the value can't be 0?
Two calculations divide by the number you enter. A part of a total of zero, or a change starting from zero, has no meaningful percentage, so the calculator says so instead of showing a made-up result.
What is the difference between percent and percentage points?
If a savings rate goes from 4% to 5%, it rose by 1 percentage point, but by 25% in relative terms. Use the percentage change section with 4 and 5 to see the second figure.
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