Percentage Calculator Formulas
The formulas you use most
Percentage math looks harder than it is because the question changes shape. The core idea is always the same: divide by 100, multiply by the base number, and compare the new value against the old value.
- X% of Y =
(X / 100) * Y - Percentage increase =
((new - old) / old) * 100 - Percentage decrease =
((old - new) / old) * 100 - What percent is A of B =
(A / B) * 100
Example: what is 20% of 150?
Convert 20% into 0.20, then multiply by 150. The answer is 30. This is the same calculation behind tax, discounts, commissions, and growth rates.
Increase vs decrease
Going from 80 to 100 is a 25% increase because the change is 20 and the original value was 80. Going from 100 to 80 is a 20% decrease because the same 20-point movement is compared against 100. The starting value matters.
Use the calculator
Open the Percentage Calculator, enter the values, and use the instant result in your report, store listing, ad campaign, or spreadsheet.
Try the Percentage Calculator →Calculate percentages online: what is X% of Y, percentage increase, and percentage decrease. Free instant percentage calculator.Frequently asked questions
Why are percent increase and percent decrease not symmetrical?
Because each one divides by a different starting value. 80 to 100 uses 80 as the base, while 100 to 80 uses 100.
How do I calculate 15% of a number quickly?
Find 10%, find 5%, then add them. For 200, 10% is 20 and 5% is 10, so 15% is 30.