Example 1, X% of Y
What is 18% of 240?
43.2
- 1
Convert percent to decimal
18% = 18 / 100 = 0.18 - 2
Multiply
0.18 × 240 = 43.2 - 3
Result
18% of 240 = 43.2
The basic form: convert percent to a decimal, then multiply.
4 Modes, Zero Maths
Percentage Calculator with Steps
Calculate percent of a number, percent change, percentage increase or decrease, and reverse percentages, all with step-by-step solutions.
Result
43.2
Computation: (18/100) × 240 = 43.2
For complex problems, use the photo solver.
How percentages work
Core Formula
X% of Y = (X / 100) × Y
Convert the percent to a decimal, multiply, done. Every percentage problem reduces to this idea with a rearrangement.
A percentage is just a fraction expressed out of 100. The symbol % literally means "per hundred," so 15% is the same as 15/100 or 0.15. Once you internalize that, every percentage problem becomes either a multiplication or a division.
The four most common percentage problems are: finding X% of a number, finding what percent one number is of another, finding the percent change between two values, and applying a percent increase or decrease. The calculator above handles all four with one click.
Worked Examples
Five percentage problems you'll actually use
From discounts and tips to grade calculations and percent change, every common scenario worked out below.
Example 2, Number as percent of another
30 is what percent of 120?
25%
- 1
Set up the ratio
30 / 120 = 0.25 - 2
Convert to percent
0.25 × 100 = 25 - 3
Result
30 is 25% of 120
Useful for grades, statistics, and survey results.
Example 3, Percent change
From 80 to 100, what is the percent change?
+25%
- 1
Find the difference
100 − 80 = 20 - 2
Divide by original
20 / 80 = 0.25 - 3
Convert to percent
0.25 × 100 = 25%
Percent change is always relative to the original value, not the new one.
Example 4, Percent increase
Increase 100 by 15%
115
- 1
Compute the increase
100 × 15/100 = 15 - 2
Add to original
100 + 15 = 115 - 3
Result
100 increased by 15% is 115
Used in pricing, taxes, and tip calculations.
Example 5, Percent decrease
Reduce 200 by 30%
140
- 1
Compute the decrease
200 × 30/100 = 60 - 2
Subtract
200 − 60 = 140 - 3
Result
200 decreased by 30% is 140
Common for discounts and reductions.
The percentage calculator that shows every step
Percentages appear in shopping discounts, taxes, tips, grades, surveys, statistics, finance, science, and everyday conversation. A clean step-by-step calculator removes ambiguity, you see the formula, the substitution, and the final value, so you can verify the math yourself and learn the pattern. This page covers the four most common percentage problems and shows worked examples for each.
How to find X% of a number
To find X% of Y, multiply Y by X divided by 100. Equivalently, write the percent as a decimal (e.g. 18% becomes 0.18) and multiply. This is the most common percent operation, used everywhere from tipping at restaurants to calculating sales tax, commissions, and discounts.
How to compute percentage change
Percentage change measures how much one value differs from another, as a fraction of the original. The formula is (new − original) / original × 100. A positive result means an increase, a negative result means a decrease. Always divide by the original value, not the new one, this is the most common mistake students make.
Percentage increase and decrease
Applying a percent increase means computing the increase amount (X × percent / 100) and adding it to the original. Percent decrease is the same operation with subtraction. A 20% increase followed by a 20% decrease does NOT bring you back to the original, this is a fun gotcha worth remembering.
Tips for using this calculator
Pick the mode that matches your problem. Enter the two numbers as plain decimals (e.g. 18 for 18%). Negative percentages and negative inputs both work. For multi-step business problems like compound discounts or markup-then-discount, run the calculator multiple times feeding the result back in.
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