Percentage Calculator

A Percentage Calculator is a free tool that solves every common percent question in one place: what X% of Y is, what percent one number is of another, the percentage increase or decrease between two values, adding or subtracting a percentage from a number, and the percentage change from an old value to a new one. Each mode is its own small block that recalculates the moment you type, with a plain worked example under every answer.

Everything runs locally in your browser with JavaScript, so results appear instantly and nothing you enter is ever sent to a server. There is no sign-up, no ads interrupting the math, and no rounding surprises.

How to use the percentage calculator

1. Pick the block that matches your question — for example, "What is X% of Y?" to find a tip or a discount amount.
2. Type your two numbers into the fields; you can use decimals and negative numbers.
3. Read the large result and the small formula line beneath it, which shows exactly how the answer was reached.
4. Change either number and the result updates live — no button to press.
5. Move to another block for a different kind of percentage problem; each one works independently.

What is a percentage?

A percentage is a ratio expressed out of 100. Writing 25% is just another way of saying 25 per 100, or the fraction 0.25. To turn a percent into a multiplier you divide by 100, and to turn a multiplier back into a percent you multiply by 100. Almost every calculation on this page is a small rearrangement of that single idea.

Percentage calculator features

• Five modes in one view — percent of a number, a number as a percent of a total, increase/decrease, add/subtract a percent, and percentage change.
• Live results that recalculate as you type, with no submit button.
• Worked-example line under each answer so you can see the formula, not just the number.
• Decimal and negative support for prices, measurements, and losses.
• Safe division handling that explains when a base of zero makes a percentage undefined.
• 100% client-side — fast, private, and usable offline once the page has loaded.

When would you use each mode?

Use "What is X% of Y?" for tips, taxes, and discounts. Use "X is what percent of Y?" to score a test result or find a completion rate — handy when you have counted items with a Word Counter and want to know what share hit a target length. The increase/decrease and percentage change blocks look similar but differ in intent: increase/decrease is best when you already know which value came first, while percentage change is framed explicitly as old versus new, which is the phrasing you want for growth rates and price movements.

Where percentages meet dates and time

Percentages often describe progress through a span of time. If you are tracking how far along a project or a subscription period you are, you can measure the elapsed span with a Date Difference Calculator and then express that as a percent of the total here. The same trick works for a lifespan or milestone: pair an Age Calculator with this tool to see, say, what percentage of a year has passed. When your raw time data is stored as epoch seconds, a Unix Timestamp Converter turns those numbers into readable dates first, so the durations you feed into a percentage make sense.

Frequently Asked Questions

How do I calculate what percent one number is of another?

Divide the part by the whole and multiply by 100. For example, 45 out of 180 is 45 ÷ 180 × 100 = 25%. The "X is what percent of Y?" block does this automatically as you type.

What is the difference between percentage increase and percentage change?

They use the same formula — (new − old) ÷ old × 100 — but the change block always labels the result relative to an explicit old and new value, including a plus or minus sign. Increase/decrease simply names the direction of the movement. Choose whichever phrasing matches how you think about the numbers.

How do I add or subtract a percentage from a number?

Multiply the number by the percent to get the amount, then add or subtract it. Adding 15% to 200 is 200 + (200 × 0.15) = 230. The add/subtract block lets you switch direction with a dropdown.

Can it handle decimals and negative numbers?

Yes. Every field accepts decimal values and negative numbers, so you can work with prices, measurements, temperatures, or losses without any special formatting.

Why does a result sometimes show a dash?

A dash appears when a calculation is undefined — most often when you try to find a percentage of a total that is zero, since dividing by zero has no meaningful answer. Enter a non-zero base and the result returns.

Is my data sent anywhere?

No. All calculations happen locally in your browser with JavaScript. Nothing is uploaded, logged, or stored, and the tool keeps working even if you go offline after the page loads.