Percentages come up everywhere — shopping discounts, exam scores, salary increases, tax calculations, and more. This tool handles three types of percentage problems that people face most often in daily life.
A percentage is simply a fraction out of 100. "25%" means 25 out of every 100. The word comes from the Latin "per centum" meaning "by the hundred". Once you understand that, all percentage problems become simple division and multiplication.
To find what percentage A is of B: divide A by B, then multiply by 100. Formula: (A / B) x 100 = percentage. For example, 25 out of 80: (25 / 80) x 100 = 31.25%. This means 25 is 31.25% of 80.
For percentage change: subtract the old value from the new value, divide by the old value, and multiply by 100. Formula: ((New - Old) / Old) x 100. For example, price rose from $50 to $65: ((65-50)/50) x 100 = 30% increase. A negative result indicates a decrease.
To find X% of a number: divide X by 100, then multiply by the number. Formula: (X / 100) x Number. For example, 15% of 200: (15 / 100) x 200 = 30. A quick mental trick: to find 10%, move the decimal point one place left; 5% is half of 10%; 20% is double 10%.
To add a percentage to a price: multiply the price by (1 + percentage/100). For example, to add 10% to $80: $80 x 1.10 = $88. To add 20%: multiply by 1.20. This is the same formula used for adding GST, VAT, tips, and markups.
If a $120 item is on sale for $90, the discount is $30. Discount percentage = (Discount / Original Price) x 100 = (30 / 120) x 100 = 25% off. To find the sale price from a percentage discount: Sale Price = Original Price x (1 - discount%/100).