Percentage Calculator
Three instant percentage calculations in one tool. Find X% of a number, compare two numbers as a percentage, or find the original from a percentage. No sign-up needed.
Type of calculation
How percentage works
A percentage is a way of expressing a number as a fraction of 100. The word "percent" comes from the Latin "per centum," meaning "by the hundred." When you say "25%," you are really saying "25 out of every 100," which in decimal form is 0.25. This tool handles all four common percentage calculations by rearranging one basic formula depending on which value you are solving for: part = whole × rate ÷ 100. Depending on the mode you select, we rearrange to solve for the part, the rate, or the whole.
In mode one (X% of Y), you multiply Y by X divided by 100. In mode two (X is what % of Y), you divide X by Y and multiply by 100. In mode three (X is Y% of what), you divide X by Y and multiply by 100 to find the original whole. In mode four (% change), the formula is ((new − old) ÷ old) × 100, which gives you the percentage increase if positive or decrease if negative.
A percentage is fundamentally different from a percentage point. If an interest rate rises from 5% to 7%, that is a 2 percentage point increase, but it is actually a 40% increase relative to the original rate. This distinction matters enormously in finance, statistics, and news reporting — a fact that even experienced professionals sometimes get wrong.
Common uses of percentage calculations
Percentage calculations appear everywhere in daily life. Shoppers use them to figure out sale prices: a 30% discount on a $80 item saves $24, bringing the price to $56. Diners calculate tips — 20% of a $47.50 bill is $9.50, giving a total of $57. Workers understand pay raises as percentages — a 5% raise on a $55,000 salary is $2,750. Investors track returns as percentages: a $1,000 investment that grows to $1,230 represents a 23% gain.
In business, percentage calculations drive margin analysis, markup pricing, year-over-year growth comparisons, and conversion rate optimization. A retailer might say conversion rate improved from 2.4% to 3.1% — that 0.7 percentage point gain represents nearly a 30% relative improvement in the effectiveness of their website. Understanding both the absolute and relative interpretation is key to making accurate business decisions.
Frequently asked questions
How do I calculate a percentage of a number?
To find X% of Y, multiply Y by X and divide by 100. For example, 15% of 80 = (80 × 15) ÷ 100 = 1,200 ÷ 100 = 12. In decimal form, this is simply 80 × 0.15 = 12. The same logic works in reverse: to express one number as a percentage of another, divide the first by the second and multiply by 100. So 30 out of 45 is (30 ÷ 45) × 100 = 66.67%.
What is the difference between percentage and percentage point?
A percentage point is the absolute difference between two percentages, while a percentage change is the relative change. If your credit card interest rate goes from 18% to 21%, that is a 3 percentage point increase. But as a percentage of the original rate, it is a (3 ÷ 18) × 100 = 16.7% increase. Financial advertisements often bury whether they are advertising a percentage point rate or a relative rate — always check which one you are reading.
How do I calculate percentage increase or decrease?
Use the % change mode in this calculator. The formula is ((new value − old value) ÷ old value) × 100. If the result is positive, it is an increase; if negative, it is a decrease. For example, a stock price rising from $50 to $65 is a ((65 − 50) ÷ 50) × 100 = 30% increase. Going the other way, if the price falls from $50 to $40, that is a −20% change.
How do I find the original number before a percentage change?
If you know the final value and the percentage change, you can work backwards. If something increased by 25% to reach $100, the original was $100 ÷ 1.25 = $80. If it decreased by 20% to reach $60, the original was $60 ÷ 0.80 = $75. This is mode three in this calculator: enter the known final value, the known percentage, and solve for the original.
Why does the third mode sometimes show strange results?
Mode three (X is Y% of what) solves for the original whole. If you enter 0 as the percentage, any number multiplied by 0 is 0, so the result is mathematically undefined — we show 0 as a safe fallback. If you enter an unusually large or small percentage, the original number may be very large or very small, which is mathematically correct but contextually unusual.
Can I use percentages to compare things of different sizes?
Yes, but only as relative changes. Comparing a $1 million gain on a $10 million investment (10%) to a $100,000 gain on a $200,000 investment (50%) shows that the smaller investment produced a far higher relative return. Percentages normalize for size, which is why they are the standard language for comparing performance across different scales — in finance, science, sports statistics, and academic grading.
What is a good tip percentage?
In the United States, 15-20% is standard for table service at restaurants. 20% is considered generous, 15% is acceptable for adequate service. For counter service or takeout, no tip or a small rounding is typical. In many European countries, a service charge is already included in the bill, so additional tipping is optional and usually 5-10%. Taxis in the US typically get 15-20%. Tipping customs vary significantly by country — always research local norms when traveling abroad.
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For general calculations only. Not financial, tax, or legal advice — see our disclaimer.