How to Calculate Percentage of a Number

Quick Answer

To find a percentage of a number, multiply the number by the percentage and divide by 100. So 15% of 80 = 80 × 15 ÷ 100 = 12. Use the free calculator at dotsapps.com for instant answers.

The Basic Percentage Formula

The formula is:

Result = Number × Percentage ÷ 100

Or move the decimal point two places left. 15% becomes 0.15. Then multiply: 80 × 0.15 = 12.

Both methods give the same answer. Use whichever feels easier.

Common Percentage Calculations

Here are percentages people calculate most often:

Tipping 15-20% — $50 meal × 0.20 = $10 tip
Sales tax 8% — $100 purchase × 0.08 = $8 tax
Discount 25% — $80 item × 0.25 = $20 off = $60 final price
Grade 85% — 85 out of 100 points
Interest 5% — $10,000 × 0.05 = $500 per year

For quick mental math with tips: find 10% (just move the decimal) and then adjust. 10% of $50 is $5. Double it for 20% = $10.

Finding What Percentage One Number Is of Another

Sometimes you need the reverse: what percentage is 30 of 200?

Percentage = (Part ÷ Whole) × 100

30 ÷ 200 = 0.15. Then 0.15 × 100 = 15%. So 30 is 15% of 200.

This comes up when calculating test scores, win rates, completion rates, and profit margins.

Percentage Increase and Decrease

To find the percentage change between two numbers:

% Change = ((New - Old) ÷ Old) × 100

Price went from $80 to $100? That is (100-80) ÷ 80 × 100 = 25% increase.

Price dropped from $100 to $80? That is (80-100) ÷ 100 × 100 = 20% decrease.

Notice these are different percentages even though the dollar amount is the same. That is because the base number changed.

How to Do It: Step-by-Step

1
Open the Percentage Calculator at dotsapps.com
2
Enter the number and the percentage you need
3
See the result instantly
4
Switch modes for percentage increase, decrease, or finding the percentage
5
Use the margin and markup calculators for business math

Try Percentage Calculator Now →

Frequently Asked Questions

What is 20% of 100?

20% of 100 is 20. Multiply 100 by 0.20 to get 20.

How do I calculate a 15% tip?

Multiply the bill by 0.15. A $50 bill gets a $7.50 tip. Quick shortcut: find 10% ($5) and add half of that ($2.50).

What is the difference between margin and markup?

Margin is profit as a percentage of the selling price. Markup is profit as a percentage of the cost. A $60 item that costs $40 has a 33% margin but a 50% markup.

How do I find what percentage one number is of another?

Divide the part by the whole and multiply by 100. For example, 25 out of 200 = 25 ÷ 200 × 100 = 12.5%.