Percentage Calculator
Find a percent of a number, compare a part with a whole, work backward to the original value, or calculate a percentage change.
Percentage Calculator
Guide
Percentage basics
A percentage tells you how many parts out of 100 you have. This calculator covers the everyday cases: a percent of a value, one number as a percent of another, the original whole, a discount, a markup, or a before-and-after change.
Use
How to use the percentage calculator
- Choose the mode that matches your question. The input labels change after you select a mode.
- Enter the two numbers you know. Use plain numbers, not the percent sign.
- Click Calculate to get the answer and the steps used to reach it.
- Use Copy result, Print, or Download TXT if you need to save the calculation.
Methods
What this calculator can solve
Percent of a value
Use this when you know the percent and the value, such as 15% of 80.
Part of a whole
Use this when you know the part and the whole, such as 30 out of 150.
Find the original value
Use this when the part and its percentage are known, such as 30 is 20% of what number.
Change, discount, or markup
Use this for price changes, growth, discounts, markups, and before-and-after comparisons.
Formula
Percentage formulas
The calculator uses the same basic idea in each mode. A percent is a value divided by 100. Percentage change is different because it compares the difference with the original value.
result = value x percentage / 100percent = part / whole x 100whole = part x 100 / percentagechange = (new value - original value) / original value x 100new value = value x (1 + percentage / 100)new value = value x (1 - percentage / 100)Examples
Example calculations
What is 20% of 150?
150 x 20 / 100 = 30
30 is what percent of 150?
30 / 150 x 100 = 20%
30 is 20% of what number?
30 x 100 / 20 = 150
Increase 150 by 20%
150 x 1.20 = 180
Decrease 150 by 20%
150 x 0.80 = 120
Change from 80 to 100
(100 - 80) / 80 x 100 = 25%
Limits
When the result needs context
A percentage can hide the size of the original number. A 50% increase from 2 to 3 is small in actual units, while a 5% change on a large bill can matter. For percent change, the original value cannot be zero because the formula divides by that starting value.
FAQ
Percentage calculator FAQ
How do I calculate a percentage of a number?
Choose What is X% of Y?, enter the percentage and the value, then calculate. The formula is value x percentage / 100.
How do I find what percent one number is of another?
Choose X is what percent of Y?, enter the part and the whole, then calculate. The calculator divides the part by the whole and multiplies by 100.
Can this calculator find the original number?
Yes. Choose X is P% of what?, then enter the known part and the percentage. The calculator works backward to the full value.
How is percentage change calculated?
Percentage change compares the difference with the original value. The formula is (new value - original value) / original value x 100.
Why does percentage change fail when the original value is zero?
The formula divides by the original value. If the original value is zero, there is no valid percentage change.
Can I calculate discounts and markups?
Yes. Use Decrease X by P% for a discount. Use Increase X by P% for a markup, growth amount, or tax-like addition.
Can I enter decimals?
Yes. Decimal values and decimal percentages are supported.