How to Calculate a Percentage — Easy Methods

A percentage is a number out of 100. To calculate a percentage, divide the part by the whole and multiply by 100 — and to find a percent of a number, multiply the number by the percentage and divide by 100. These two moves cover almost every percentage question you will meet: tips, discounts, price rises, exam scores and interest.

By Calcly Team · Last updated 6 November 2026 · Free guide

What is a percentage, really?

The word percent means “per hundred”, and the symbol % is shorthand for “out of 100”. So 25% means 25 out of every 100, 50% means half, and 100% means the whole thing. That simple idea is the key to every method below: whenever you are stuck, ask yourself “out of 100, how many is this?” Percentages are used everywhere because they let you compare things of different sizes fairly. A score of 18 out of 20 and a score of 45 out of 50 look hard to compare, but as percentages they are 90% and 90% — exactly the same result. A shop discount of 30% means the same saving rate whether the item costs $20 or $200, even though the cash saving is different. Once you can move between a fraction, a decimal and a percentage, the rest is arithmetic you already know.

It helps to remember three quick conversions. To turn a percentage into a decimal, divide by 100 — so 25% becomes 0.25 and 7.5% becomes 0.075. To turn a decimal into a percentage, multiply by 100 — so 0.6 becomes 60%. And to turn a fraction into a percentage, divide the top number by the bottom number and multiply by 100 — so 3 out of 4 is 3 ÷ 4 × 100 = 75%. Keep those three moves in mind and every worked example below will feel familiar.

Method 1: Finding a percent of a number

This is the most common percentage question: what is 25% of 200? What is 15% of 80? The formula is simple: percent of a number = number × percentage ÷ 100. So 25% of 200 is 200 × 25 ÷ 100 = 50. And 15% of 80 is 80 × 15 ÷ 100 = 12. Try it with a restaurant bill: a meal costs $80 and you want to leave a 20% tip. The tip is 80 × 20 ÷ 100 = $16, so the total is $96. The same method works for a pay rise: a $2,000 monthly salary with a 5% rise gains 2,000 × 5 ÷ 100 = $100, taking the new salary to $2,100. If the percentage is awkward, use the 10% trick first: 10% of any number is the number with the decimal point moved one place left, so 10% of 240 is 24. From there, 5% is half of 10% (12), 20% is double 10% (48), and 30% is three times 10% (72). You can reach most everyday percentages by adding a few of these building blocks together, which is often faster than reaching for a calculator.

Method 2: What percent is one number of another?

Sometimes you know both numbers and want the percentage between them: what percent is 25 of 200? What did you score if you got 45 out of 50? The formula is: percentage = (part ÷ whole) × 100. So 25 is 12.5% of 200, because 25 ÷ 200 = 0.125 and 0.125 × 100 = 12.5. A score of 45 out of 50 is 45 ÷ 50 × 100 = 90%. This method also answers questions like “what share of my income goes on rent?” If you earn $4,000 a month and pay $1,200 in rent, rent is 1,200 ÷ 4,000 × 100 = 30% of your income. And it works for progress: if you have saved $3,000 towards a $12,000 goal, you are 3,000 ÷ 12,000 × 100 = 25% of the way there. A common mistake here is dividing the wrong way round — always divide the smaller, part number by the larger, whole number. If your answer comes out above 100% when you expected less, you have probably divided the whole by the part instead of the part by the whole.

Method 3: Percentage increase and decrease

Price rises, pay rises and falling values all use one formula: percentage change = ((new value − old value) ÷ old value) × 100. If a price rises from $80 to $100, the change is (100 − 80) ÷ 80 × 100 = 20 ÷ 80 × 100 = 25%, so a 25% increase. If a value falls from 200 to 150, the change is (150 − 200) ÷ 200 × 100 = −50 ÷ 200 × 100 = −25%, so a 25% decrease. The sign tells you the direction: a positive answer is an increase and a negative answer is a decrease. One thing that catches people out is that a 50% rise followed by a 50% fall does not take you back to where you started. A $100 item rising 50% becomes $150, and then falling 50% takes off $75, leaving $75 — not $100. That is because the second percentage is taken from a different, larger starting value. The same logic applies to investments and sale prices, so always check which value the percentage is being taken from.

Method 4: Discounts and sale prices

A discount question is just Method 1 in reverse. If a $120 jacket is 30% off, the saving is 120 × 30 ÷ 100 = $36, so you pay $120 − $36 = $84. A shortcut is to work out what you actually pay: 100% − 30% = 70%, so the sale price is 120 × 70 ÷ 100 = $84 in one step. To find the discount percentage from two prices, use Method 2: a $100 item on sale for $75 has saved $25, which is 25 ÷ 100 × 100 = 25% off. Shops sometimes stack discounts, and here the order does not matter but the percentages do not simply add up: 20% off followed by a further 10% off is not 30% off. A $100 item becomes $80 after the first discount, and 10% off $80 is $8, so you pay $72 — a total saving of 28%, not 30%. If you want to check any of these numbers instantly, try our percentage calculator — it has a mode for each method on this page.

Common percentage mistakes to avoid

Three mistakes cause most wrong answers. First, mixing up percentage points and percent: if an interest rate rises from 4% to 6%, that is a rise of 2 percentage points, but a 50% increase in the rate itself — the two phrases mean different things. Second, forgetting which number is the whole: in “what percent is 30 of 120?”, the whole is 120, so the answer is 30 ÷ 120 × 100 = 25%; dividing 120 by 30 instead gives a meaningless 400%. Third, rounding too early: keep two or three extra digits while you work and round only at the end, especially with money, where a few cents matter. If a result looks wrong, sanity-check it — 25% of 200 must be 50, not 500, and a 10% tip on $80 must be $8, not $80.

Want the answers without the arithmetic? Use our percentage calculator for any of these methods, our tip calculator for restaurant bills and bill splits, or our loan calculator to see how percentages become real monthly payments.