How to Calculate Percentage

A percentage is a way to express a number as a fraction of 100. The word percent comes from the Latin “per centum”, which means “per hundred”. When you see 50%, it literally means 50 out of every 100, or 50 divided by 100.

Percentages are everywhere in daily life: sales discounts, test scores, interest rates, statistics, growth rates, and much more. Understanding percentages helps you make better financial decisions, interpret data correctly, and solve everyday math problems quickly.

There are four main types of percentage calculations you will encounter. Here are the formulas for each:

These tricks will help you calculate percentages quickly in your head without a calculator:

• 10% trick: Move the decimal point one place left. 10% of 250 = 25
• 5% trick: Find 10% then divide by 2. 5% of 80 = (8) / 2 = 4
• 1% trick: Move the decimal point two places left. 1% of 350 = 3.5
• 50% trick: Simply divide by 2. 50% of 88 = 44
• 25% trick: Divide by 4. 25% of 120 = 30
• 15% tip trick: Find 10%, then add half of that. 15% of $40 = $4 + $2 = $6
• 20% trick: Divide by 5. 20% of 75 = 15
• Reversible percentages: 8% of 50 is the same as 50% of 8 (both equal 4)

• Confusing percentage increase with percentage points: Going from 20% to 30% is a 50% increase, not a 10% increase. The difference in percentage points is 10, but the percentage increase is 50%.
• Forgetting order matters: A 50% increase followed by a 50% decrease does NOT return to the original value. If something goes from $100 to $150 then down 50%, it ends at $75, not $100.
• Mixing up part and whole: Make sure you are dividing by the correct number. To find what percent 20 is of 80, divide 20 by 80, not 80 by 20.
• Incorrectly stacking discounts: A 20% discount plus a 30% discount is NOT a 50% discount. They multiply: 0.8 x 0.7 = 0.56, which is a 44% total discount.
• Using the wrong base: For percentage change, always divide by the original (old) value, not the new value.

• Shopping: To quickly calculate a 30% discount, find 10% of the price and multiply by 3, then subtract from the original price.
• Tipping: For a 20% tip, move the decimal left one place (10%) and double it. For 15%, do 10% plus half of that.
• Comparing deals: Convert all discounts to percentages to compare apples to apples. A $20 discount on a $100 item (20%) is better than a $30 discount on a $200 item (15%).
• Interest rates: Remember compound interest grows exponentially. A 5% annual return doubles your money in about 14 years.
• Test scores: To convert a fraction to a percentage, divide the score by the total and multiply by 100. Or use our Percent Calculator to check the answer instantly.