A percentage calculator is a free online tool that solves any percentage problem instantly — no pencil, paper, or mental arithmetic required. Whether you need to find what 20% of 150 is, calculate how much a price changed, figure out your server's tip, or work out the sales tax on a purchase, a good percentage calculator gives you the answer in milliseconds.

On this site you'll find ten specialist percentage calculators, each built for a specific type of problem. Every tool shows the result as you type, displays the formula with your numbers substituted in, walks you through the calculation step-by-step, and renders a visual bar so you can see the percentage at a glance.

How to calculate a percentage

The core formula is simple: Result = (Percentage ÷ 100) × Number. To find 25% of 200, divide 25 by 100 to get 0.25, then multiply by 200 to get 50. Every other percentage calculation builds on this foundation.

For percentage change, subtract the old value from the new, divide by the absolute old value, and multiply by 100. A result above zero is an increase; below zero is a decrease. For a reverse percentage — finding the original value before a percentage was applied — divide the result by the percentage expressed as a decimal: Original = Final ÷ (Percentage ÷ 100).

The 10 percentage calculators on this site

Percentage Calculator — What is X% of Y?

The most common percentage calculation. Enter any percentage and number to get an instant result. Used for working out discounts, tax amounts, tips, grades, and more.

Percentage Change Calculator

Calculates the percentage increase or decrease between two values. Shows a colour-coded before/after comparison so you can see the direction of change at a glance.

Reverse Percentage Calculator

Works backwards from a percentage result to find the original value. Useful for finding the pre-discount price of a sale item or the pre-tax price of a receipt total.

Percentage Difference Calculator

Compares two values symmetrically using their average as the reference point — neither value is treated as "before" or "after". Ideal for comparing two measurements or survey results.

Percentage Increase / Decrease Calculator

Applies a known percentage increase or decrease to a starting value. Switch between increase and decrease mode with a single click.

What Percent of X is Y?

Finds what percentage one number is of another. For example: 50 is what percent of 200? Answer: 25%.

Percentage Error Calculator

Measures how far an experimental or estimated value is from the true value, expressed as a percentage. Widely used in science, engineering, and statistics.

Tip Calculator

Calculates the tip amount on any bill and splits the total evenly between any number of people. Choose from quick presets — 10%, 15%, 18%, 20%, 25% — or enter a custom percentage.

Discount Calculator

Finds the sale price and the amount saved after any percentage discount. Quick-select buttons for the most common discounts — 5% off through 50% off.

Sales Tax Calculator

Adds sales tax to a price or strips tax from a total to find the pre-tax amount. Includes quick-pick buttons for common US state tax rates including California (7.25%), Texas (6.25%), New York (4%), and more.

Real-world uses for a percentage calculator

Shopping and finance. Use the discount calculator to see exactly how much you save on a sale item. Use the sales tax calculator to find the final price including tax before you reach the checkout. Use the percentage change calculator to see whether your investment portfolio has grown or shrunk.

Eating out. The tip calculator removes the awkward arithmetic at the end of a meal. Enter the bill, choose your tip percentage, and split evenly among the table in one step.

School and work. The percentage error calculator is essential for lab reports and data analysis. The percentage difference calculator compares survey responses, A/B test results, or any two data points. And the basic percentage calculator handles every "what is X% of Y?" question that comes up in day-to-day work.

All tools on Percentage Calc Tools are completely free, require no account or sign-up, and work on any device. Results appear instantly as you type — there is no submit button. Each calculator also shows the formula it used and walks you through the calculation step-by-step, so you not only get your answer but understand how it was reached.

Frequently asked questions.

What is a percentage calculator?

A percentage calculator is a free online tool that solves percentage problems instantly — such as finding what X% of a number is, calculating how much a value changed, or working out a discount or tip amount.

How do I calculate a percentage of a number?

Use the formula: Result = (Percentage ÷ 100) × Number. For example, 25% of 200 = (25 ÷ 100) × 200 = 50. Our percentage calculator does this instantly as you type.

How do I calculate percentage change?

Percentage change = ((New Value − Old Value) ÷ Old Value) × 100. A positive result is a percentage increase; negative is a decrease. Use our percentage change calculator for instant results.

How do I calculate a tip?

Tip = Bill Amount × (Tip % ÷ 100). For a 20% tip on a $50 bill: $50 × 0.20 = $10. Our tip calculator also splits the total between any number of people.

How do I calculate a discount?

Sale Price = Original Price × (1 − Discount% ÷ 100). For 30% off $120: $120 × 0.70 = $84. Use our discount calculator with quick-select presets from 5% to 50% off.

How do I add sales tax to a price?

Total = Price × (1 + Tax Rate ÷ 100). For an 8% tax on $99: $99 × 1.08 = $106.92. Our sales tax calculator includes common US state tax rates.

What is the difference between percentage change and percentage difference?

Percentage change is directional — it measures from an old value to a new one. Percentage difference is symmetric — it compares two values using their average as the reference, with neither value treated as "before" or "after."

Are all the percentage calculators on this site free?

Yes. All 10 tools are completely free to use with no account, sign-up, or payment required. Results appear instantly as you type on any device.