How to Calculate Percentages (The 3 Types People Actually Need)

Type 1: Find a percent of a number

This is the most common: you have a number and you want a percentage of it. Discounts, tips, tax, and commission all work this way.

Example: 20% of 150. (20 / 100) x 150 = 0.2 x 150 = 30. A quick shortcut: 10% of any number is just the number with the decimal moved one place left (10% of 150 = 15), so 20% is double that (30).

Type 2: Find what percent one number is of another

Use this when you have two numbers and want the ratio as a percentage: a test score, a completion rate, or what share of revenue a cost represents.

Example: you sold 45 of 60 tickets. (45 / 60) x 100 = 75%. Make sure the smaller number (the part) goes on top and the total (the whole) goes on the bottom, or the answer flips.

Type 3: Find the percentage change

Use this for growth or drop between two points in time: price changes, revenue growth, or audience increases.

Example: revenue went from 8,000 to 10,000. ((10,000 - 8,000) / 8,000) x 100 = (2,000 / 8,000) x 100 = 25% increase. A negative result means a decrease. Always divide by the old (starting) value, not the new one.

Markup is not the same as margin

A common trap: a 40% markup does not give a 40% margin. Markup is profit as a percent of cost; margin is profit as a percent of price. A product costing 100 sold for 140 has a 40% markup but only a 28.6% margin. If you price products, know which one you mean.

Reverse percentages

Sometimes you know the result and need the original. If a price of 120 already includes 20% tax, do not subtract 20%. Divide by 1.20 instead: 120 / 1.20 = 100 net, so the tax was 20. Subtracting 20% of 120 (24) would give the wrong answer because the 20% was added to the smaller net figure, not the larger gross one.

Use the Percentage Calculator

The Percentage Calculator handles all three types in one place, plus percentage increase, decrease, and reverse percentages. Enter your numbers and read the result with the calculation shown, so you can check the working rather than trust a black box.

Frequently asked questions

How do I work out a percentage in my head?

Start from 10% (move the decimal one place left), then scale. For 15% of 80: 10% is 8, 5% is half of that (4), so 15% is 12. For 20%, double the 10%. This covers tips and quick discounts without a calculator.

What if the percentage is over 100%?

The same formulas work. 150% of 200 is (150 / 100) x 200 = 300. A percentage change over 100% means something more than doubled: going from 50 to 130 is a 160% increase.