Percentage Calculator
Calculate a percentage of a number, find what percent one value is of another, or measure percentage increase and decrease.
Use the Percentage Calculator for the three percentage questions that appear most often in everyday work: finding a percentage of a value, finding what percentage one value represents of another, and calculating percentage change between an old and new value. The formulas are simple once you know which number belongs in the denominator, so use the supporting guide if you want to see the arithmetic instead of only the result.
- three percentage formulas you will actually use
- Discount Calculator
- Profit Margin Calculator
- How to Check an Online Calculator
Calculate the percentage you actually need
Percentage questions look similar, but they are not all the same calculation. This tool handles the three versions people run into most often: finding a percentage of a number, finding what percentage one number is of another, and measuring percentage change between an old and new value.
Three common percentage calculations
What is 15% of 80?
Convert 15% to 0.15 and multiply: 80 × 0.15 = 12. This is useful for discounts, tips, tax estimates, commissions, and portions of a total.
18 is what percent of 72?
Divide the part by the whole and multiply by 100: 18 ÷ 72 × 100 = 25%. This is useful for completion rates, scores, conversion rates, and comparing a part with a total.
What is the percentage change from 80 to 100?
Subtract the starting value, divide by the starting value, and multiply by 100: (100 − 80) ÷ 80 × 100 = 25%.
Why increases and decreases are not symmetrical
A 25% increase followed by a 25% decrease does not return to the starting value. If 100 increases by 25%, it becomes 125. Reducing 125 by 25% removes 31.25, leaving 93.75. The second percentage is calculated from a different base.
When to double-check the result
Percentage math is straightforward, but the difficult part is often choosing the correct starting value. For growth, decline, returns, or price changes, confirm which value is the original baseline before calculating.
Frequently asked questions
How do I add 20% to a number?
Multiply the number by 1.20. For example, 50 × 1.20 = 60.
How do I remove 20% from a number?
Multiply by 0.80. That subtracts 20% of the original value.
Can I reverse a percentage increase?
Not by subtracting the same percentage. To reverse a 20% increase, divide the increased value by 1.20.