Percentage Calculator

How to use this tool

Choose one of the calculation modes above (X% of Y, What percent?, or % change), enter two finite numbers, and calculate the exact percentage, proportion, or relative change locally in your browser. If you only need directional rate changes, you can also jump straight to the dedicated Percentage Increase Calculator or Percentage Decrease Calculator.

Transparent method: all 4 percentage formulas at a glance

Whether you are calculating a store discount, tipping on a restaurant bill, grading a test, or comparing year-over-year revenue, nearly every percentage question uses one of four core equations:

How do you calculate a percentage of a number? (e.g., 20% of a number)

To calculate a percentage of any number, divide the percentage by 100 to convert it into a decimal, then multiply by the number:

Formula: Result = (P ÷ 100) × Y

Example (How to calculate 20% of 150): Convert 20% to 0.20, then multiply 0.20 × 150 = 30.

Mental math shortcut for 10%, 5%, and 20%: To find 10% of any number in your head, simply move the decimal point one place to the left (10% of $85.00 is $8.50). Double that number to get 20% ($17.00), or cut the 10% figure in half to get 5% ($4.25).

Quick-reference table: decimal to percentage and fraction conversions

Use this reference table when converting between decimals, percentages, and everyday fractions:

How do you calculate what percentage one number is of another number?

When you know the part and the total (whole)—for example, you scored 42 points out of 50 on an exam, or you spent $1,400 out of a $4,000 monthly paycheck on rent—divide the part by the whole and multiply by 100:

Formula: Percentage (%) = (Part ÷ Whole) × 100

Worked example 1 (Part smaller than whole): What percentage is 42 out of 50? Divide 42 ÷ 50 = 0.84, then multiply 0.84 × 100 = 84%.

Worked example 2 (Part larger than whole): What percentage is 180 out of 120? Divide 180 ÷ 120 = 1.50, then multiply 1.50 × 100 = 150%.

Important denominator rule: The whole (Y) can never be 0, because dividing any number by zero is mathematically undefined.

If you are using this formula to check what percentage of your take-home pay goes toward rent, groceries, and savings, compare your numbers against the 50/30/20 framework in our guide to budget calculators vs. monthly worksheets.

How to calculate percentage increase, decrease, and difference between two numbers

People frequently confuse percentage change (increase/decrease over time) with percentage difference (comparing two peers with no chronological "old" or "new" baseline):

Use Percentage Change (Increase or Decrease) when there is a "Before" (Original) and "After" (New) value:

Percentage Increase: If your monthly subscription rises from $40 (Original) to $50 (New), subtract 50 − 40 = +10, divide by the original baseline 10 ÷ 40 = 0.25, and multiply by 100 to get a +25% increase.

Percentage Decrease: If a jacket drops from $80 (Original) to $60 (New), subtract 60 − 80 = −20, divide by the original price −20 ÷ 80 = −0.25, and multiply by 100 to get a 25% decrease (−25%).

Use Percentage Difference when neither number is the "starting" value:

If Store A sells a laptop for $600 and Store B sells it for $660, neither store is "first." Divide the absolute gap (|600 − 660| = 60) by the average of the two prices ((600 + 660) ÷ 2 = 630), then multiply by 100: (60 ÷ 630) × 100 = 9.52% difference.

Never confuse Percent Change with Percentage Points:

As statistical agencies like the U.S. Bureau of Labor Statistics (BLS) emphasize, if a mortgage interest rate rises from 4.0% to 5.0%, it has risen by 1.0 percentage point (100 basis points), which is a 25% relative increase ((5 − 4) ÷ 4 × 100 = 25%).

Why equal percentage increases and decreases do not cancel out

A 20% increase followed by a 20% decrease does not bring you back to your starting number, because the second percentage is calculated against a new, larger denominator:

Start with $100 and increase it by 20%: $100 + ($100 × 0.20) = $120.

Now decrease $120 by 20%: $120 − ($120 × 0.20) = $120 − $24 = $96 (you are $4 below where you started).

Similarly, if an investment portfolio drops 50% from $1,000 to $500, it requires a +100% gain ($500 ÷ $500 × 100) just to get back to $1,000.

Assumptions and limits

• Inputs may be positive, zero or negative.
• Results are displayed with up to six decimal places.
• A whole or original value of zero cannot be used as a denominator.
• Percentage change divides by the absolute original value so negative starting values follow the same consistent formula.

Sources

• How the Government Measures Unemployment — Rate Changes & Percentage Points
• Format Numbers as Percentages in Excel