Find a percentage, a percent of, or percentage change.
Most real-world percentage questions fall into three types: finding what X% of a number is (like a 20% tip on a $45 bill), finding what percent one number is of another (like what percent 45 is of 180), and finding the percentage change between two values (like a price that moved from $50 to $65). This calculator handles all three modes separately, since each uses a different formula, and mixing them up is the single most common source of percentage calculation mistakes people make by hand.
'X% of Y' is simply (X ÷ 100) × Y. 'What percent is X of Y' is (X ÷ Y) × 100. And percentage change from an old value to a new value is ((New − Old) ÷ Old) × 100, where a positive result means an increase and a negative result means a decrease. That last formula trips people up most often because the denominator must always be the original (old) value, not the new one — dividing by the wrong number gives a plausible-looking but incorrect answer.
A subtle but important distinction: if interest rate moves from 5% to 7%, that's a 2 percentage point increase, but it's actually a 40% percentage increase relative to the original 5% ((7-5)/5 × 100). News headlines frequently blur this distinction, which can make a change sound smaller or larger than it actually is depending on which framing is used. This calculator's 'percentage change' mode always gives you the true percentage increase or decrease — the relative change — not the raw point difference.
This tool comes in handy for calculating tips and splitting bills, figuring out a discount's real dollar value during a sale, comparing salary raises or price changes year over year, working out grade percentages from a test score, and checking whether a 'X% off' promotion actually beats a competing flat-dollar discount. Because percentage math shows up constantly in shopping, finance, and school, having one reliable tool for all three calculation types removes the guesswork of which formula applies to which situation.
Divide the percentage by 100 and multiply by the number — for example, 20% of 50 is (20÷100) × 50 = 10.
Subtract the old value from the new value, divide by the old value, then multiply by 100 — always divide by the original number, not the new one.
Divide X by Y and multiply by 100 — for example, 45 is 25% of 180 because (45÷180) × 100 = 25.
Percentage points are the raw difference between two percentages (5% to 7% is 2 points), while percentage change is the relative change (that same move is a 40% increase).
Yes — if the new value is lower than the old value, the result displays as a negative percentage, representing a decrease.