Percentage Calculator
Calculate what X% of Y is, what percent X is of Y, or the percent change/increase/decrease between two numbers.
- Whole (B)150
- 20% of B30
20% of 150 is 30 — see how that slice sizes up against the whole.
ƒShow your work
- 120% × 150 = 30
About the Percentage Calculator
Percentages show up long before anyone calls it math class: a shopper working out whether 30% off is actually a better deal than $20 off, a server splitting a bill and adding a tip, a student checking a homework answer against the textbook, a manager reading a spreadsheet that reports growth as a percentage instead of raw numbers. The underlying operation is always the same — comparing a part to a whole, or comparing two wholes to each other — but the phrasing of the question changes depending on what you already know and what you're solving for.
That's why this calculator has three modes instead of one formula box. 'A% of B' answers the most common question — what is 20% of 150. 'A is what % of B' flips it around, for when you know both numbers and want the percentage itself, like figuring out what share of a budget a $340 expense represents. 'Percent change' handles before-and-after comparisons — a price that moved, a stat that grew or shrank — and reports it correctly signed as an increase or decrease.
People land here from a wide range of situations: a student checking arithmetic, a shopper price-comparing, someone tracking a fitness or savings goal expressed as a percentage. The math is genuinely simple once you see which of the three shapes your question is, which is really the point of splitting it out this way.
How it’s calculated
'A% of B' is a straight multiplication: convert the percentage to a decimal by dividing by 100, then multiply by B. 20% of 150 becomes (20/100) × 150 = 30.
'A is what % of B' runs that in reverse: divide A by B, then multiply by 100 to express the result as a percentage. If 30 out of 150 people answered yes, that's (30/150) × 100 = 20%.
'Percent change' compares two values relative to the starting one: (B − A) / |A| × 100. Dividing by the absolute value of A keeps the sign meaningful even when A is negative, and a positive result means an increase while a negative result means a decrease. Going from 150 to 180 is a change of (180 − 150)/150 × 100 = 20% — a 20% increase.
Frequently asked questions
How do I calculate a percentage increase?
Subtract the original value from the new value, divide that difference by the original value, then multiply by 100. This calculator's 'percent change' mode does exactly this and labels the result as an increase or decrease automatically.
What's the difference between percent change and percentage points?
Percent change is relative — going from 10% to 15% is a 50% increase relative to the starting 10%. Percentage points is the raw difference — that same move is a 5 percentage point increase. Mixing the two up is one of the most common percentage errors in news reporting and finance.
How do I find the original price before a discount?
If you know the sale price and the discount percentage, divide the sale price by (1 − discount as a decimal). A $60 item at 25% off means the original price was 60 / 0.75 = $80.
How do I convert a fraction to a percentage?
Divide the numerator by the denominator, then multiply by 100. 3/8 becomes (3 ÷ 8) × 100 = 37.5%. That's exactly what the 'A is what % of B' mode does with A as the numerator and B as the denominator.
Why can a percent change be over 100%?
Because percent change is relative to the starting value, not capped at the size of the ending value. Going from 10 to 25 is a 150% increase — the value more than doubled plus a bit more, and the formula just reports that faithfully.
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