Ten percentage calculation modes covering everyday math, tipping, discounts, markup, margin, tax, and fraction conversions. Every calculation runs in your browser as you type. Nothing is sent to a server.
A percentage is a number expressed as a fraction of 100. The word itself comes from the Latin per centum, meaning "by the hundred." When you see 25%, it means 25 out of every 100, or equivalently 0.25 as a decimal, or 1/4 as a fraction. These three representations are interchangeable, and converting between them is one of the most common tasks in everyday math.
Percentages appear constantly in daily life: sales tax, restaurant tips, exam scores, investment returns, inflation rates, battery charge levels, probability forecasts, nutritional labels. The reason they are so widespread is that they normalize different quantities to a common scale. Comparing 18 out of 24 to 45 out of 60 takes mental effort. Comparing 75% to 75% does not.
This calculator covers ten distinct percentage operations. Rather than forcing you to rearrange formulas yourself, each mode accepts plain inputs and gives you the answer instantly. Every calculation happens in your browser using JavaScript. No data leaves your device.
Three fundamental formulas cover most percentage problems:
This handles the question "what is X% of Y?" and is the basis of the first calculator card above. If you need to find 15% of 200, you compute (15 / 100) x 200 = 30.
This answers "X is what percent of Y?" It is the inverse of the first formula. If 30 is the part and 200 is the whole, you get (30 / 200) x 100 = 15%.
This measures how much a value has increased or decreased relative to its original size. A move from 80 to 100 is a 25% increase. A move from 100 to 80 is a 20% decrease. Note the asymmetry: the same absolute change (20) produces different percentages depending on the starting value. This is a common source of confusion and exactly why the percentage change calculator shows the direction alongside the number.
Percentage change compares two values and expresses the difference as a proportion of the original. The formula divides the absolute difference by the original value, then multiplies by 100.
Suppose a stock price moved from $40 to $52. The change is $12. Dividing $12 by the original $40 gives 0.3. Multiplied by 100, that is a 30% increase. If the price later drops from $52 back to $40, the change is still $12, but now you divide by $52 (the new "old" value), giving 23.08%. The trip up was 30%, but the trip down was only 23.08%. This asymmetry trips people up regularly, and it is mathematically correct.
Percentage change is used extensively in finance (stock returns, revenue growth), economics (inflation, GDP growth), science (measurement changes), and everyday contexts like comparing prices or grades. The calculator above handles the direction for you, coloring increases green and decreases red so the result is immediately clear.
Markup and margin both describe the relationship between cost and selling price, but they use different denominators. This distinction confuses even experienced businesspeople.
Markup is the percentage added to cost to get the selling price. If an item costs $50 and you apply a 60% markup, the selling price is $50 + ($50 x 0.60) = $80. The profit is $30. Markup is calculated relative to cost.
Margin is the percentage of revenue that is profit. Using the same numbers: revenue is $80, cost is $50, profit is $30. Margin = ($30 / $80) x 100 = 37.5%. Margin is calculated relative to revenue.
The same transaction produces a 60% markup but only a 37.5% margin. Markup is always higher than margin for the same sale because it uses the smaller number (cost) as the denominator. Converting between them requires care:
A 50% markup equals a 33.3% margin. A 100% markup equals a 50% margin. A 50% margin requires a 100% markup. Retailers, wholesalers, and SaaS companies all need to keep these straight when pricing products. Use the markup and margin calculators above to convert between them without memorizing the formulas.
Calculating percentages in your head is faster than reaching for a calculator in most everyday situations. A few techniques make it simple.
To find 10% of any number, move the decimal point one place left. 10% of 85 is 8.5. 10% of 230 is 23. From there, you can derive other percentages by addition or halving. 5% is half of 10%. 20% is double 10%. 15% is 10% plus 5%. This covers most tipping scenarios.
For 1%, move the decimal two places left. 1% of 850 is 8.5. You can then multiply by whatever factor you need: 3% of 850 is 3 x 8.5 = 25.5.
The commutative property of percentages is useful: X% of Y equals Y% of X. So 8% of 50 is the same as 50% of 8, which is 4. Similarly, 4% of 75 equals 75% of 4, which is 3. Look for the easier direction and compute that one instead.
For discounts, subtract from 100% first. A 30% discount means you pay 70%. To find 70% of $120: 10% is $12, so 70% is $84. Or: 120 x 0.7 = 84. Either way, $84 is the final price. This avoids the extra step of calculating the discount amount and then subtracting.
Divide the percentage by 100, then multiply by the number. For example, 15% of 200 is (15 / 100) x 200 = 30. The first calculator card on this page does this automatically as you type. Enter the percentage and the number, and the result appears instantly.
Markup is calculated as a percentage of cost, while margin is calculated as a percentage of revenue (selling price). A product that costs $50 and sells for $80 has a 60% markup (profit / cost = 30/50) but only a 37.5% margin (profit / revenue = 30/80). Markup is always a higher number than margin for the same transaction.
Percentage change divides by the starting value, and the starting value is different depending on the direction. Going from 100 to 120 is a 20% increase (20/100). Going from 120 to 100 is only a 16.67% decrease (20/120). The same absolute difference of 20 produces different percentages because the base of the calculation changes.
Divide the numerator by the denominator, then multiply by 100. For example, 3/8 = 0.375, and 0.375 x 100 = 37.5%. The fraction-to-percent card on this page handles this conversion automatically. Enter the numerator and denominator and the percentage appears.
Multiply the bill amount by the tip percentage divided by 100. For an $85 bill with an 18% tip: 85 x 0.18 = $15.30. The total becomes $100.30. If splitting between two people, each pays $50.15. For mental math, find 10% ($8.50), then add about half of that for roughly 15%, or double 10% for 20%.
Yes. All calculations run entirely in your web browser using JavaScript. No data is transmitted to any server, no information is stored, and no cookies are set. You can verify this by opening your browser's developer tools and monitoring the Network tab while using any of the ten calculators. Your inputs never leave your device.