Percentage Calculator: Free Percent of a Number

What is 20% of 85?

17

20% of 85 = 17

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How to use this percentage calculator

Pick a calculation. The four tabs cover the four questions people ask: a percentage of a number, one number as a percent of another, percentage change, and percentage difference.
Type your two numbers. The answer updates as you type — there is no Calculate button to press.
Read the answer and the working. The big number is the result; the steps under it show exactly how it was reached, so you can check it or reuse the method on paper.
Copy the result if you need it elsewhere. Nothing you type is sent or stored — the maths runs entirely in your browser.

The formulas, in plain words

A percentage is a fraction out of 100. “Percent” literally means “per hundred”, so 20% is 20 out of 100, or 0.20 as a decimal. Every percentage calculation is built from that one idea:

Percentage of a number

(Percent ÷ 100) × Number

Example: 20% of 85 → (20 ÷ 100) × 85 = 0.20 × 85 = 17. This is the formula behind tips, discounts and tax amounts.

One number as a percent of another

(Part ÷ Whole) × 100

Example: 45 out of 60 → (45 ÷ 60) × 100 = 0.75 × 100 = 75%. Test scores, completion rates and survey results all use this one.

Percentage change

((New − Old) ÷ Old) × 100

Example: $80 rising to $100 → ((100 − 80) ÷ 80) × 100 = +25%. A negative answer means a decrease. Prices, weights and salaries are compared this way. For the full guide, use the dedicated Percentage Change Calculator.

Percentage difference

(|A − B| ÷ Average of A and B) × 100

Example: 80 vs 100 → (20 ÷ 90) × 100 = 22.22%. Use this when neither number is “the original” — comparing two measurements, quotes or readings. For the full guide, use the dedicated Percentage Difference Calculator.

Change or difference? They sound alike but answer different questions. Percentage change compares a new value with the original it grew or shrank from, so order matters. Percentage difference compares two values as equals, using their average — order does not matter.

Everyday examples

Question	Calculation	Answer
20% of 85	0.20 × 85	17
45 correct answers out of 60	45 ÷ 60 × 100	75%
15% tip on a $64 bill	0.15 × 64	$9.60 (total $73.60)
30% discount on $250	0.30 × 250	You save $75, you pay $175
8% sales tax on $49.99	0.08 × 49.99	$4.00 (total $53.99)
38 correct answers out of 50	38 ÷ 50 × 100	76%

Every row loads into the calculator above if you use the matching tab — the steps shown there walk through the same arithmetic.

Frequently asked questions

What is a percentage, in plain terms?

A percentage is a number out of 100. 20% means 20 for every 100 — so 20% of 85 is 17, because (20 ÷ 100) × 85 = 17.

How do I calculate a percentage of a number?

Divide the percent by 100, then multiply by the number. For example, 20% of 85 is (20 ÷ 100) × 85 = 17. The “% of a number” tab above does exactly this and shows each step.

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

Divide the first number by the second, then multiply by 100. For example, 45 out of 60 is (45 ÷ 60) × 100 = 75%. Use the “What % is…” tab.

How do I work out a tip, a discount, or tax?

All three are a percentage of a number. A 20% tip on $85 is $17, making $102 in total. A 25% discount on $120 takes $30 off, so you pay $90. An 8% tax on $49.99 adds $4.00, for a total of $53.99.

What is the difference between percentage change and percentage difference?

Percentage change compares a new value against the original value it changed from, so it has a direction — up or down. Percentage difference compares two values as equals, dividing by their average instead, so the order you enter them in does not matter. Each has its own dedicated calculator, linked under Related tools below.

Is this calculator free, and are my numbers stored?

Yes, it is free, with no sign-up. Your numbers are never sent or stored: every calculation runs in your own browser, and the page works the same way offline once it has loaded.