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Percentage Calculator

Find X% of a number, a percent of a total, or % change

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How to use

  1. 1.Choose a mode: 'X% of Y' to find a percentage of a number, 'X is what % of Y' to turn two numbers into a percent, or '% change' to compare a before and after value.
  2. 2.Type your two numbers into the fields — the labels update to match the mode you picked, and negative numbers are allowed.
  3. 3.Read the answer and the worked formula, which update instantly below as you type — no button to press and nothing sent to a server.

About Percentage Calculator

A percentage calculator answers the three questions people actually ask about percentages, and this one handles all of them in one place: what is X% of a number, what percent one number is of another, and the percentage increase or decrease from one value to the next. Pick a mode, type two numbers, and the answer plus the worked formula appear the moment you finish typing — there is no button to press and nothing is sent to a server, because every calculation runs in your browser.

The first mode, 'X% of Y', finds a part of a whole. It multiplies the percentage by the number using the formula (X ÷ 100) × Y, so 15% of 200 is (15 ÷ 100) × 200 = 30. This is the calculation behind a store discount (20% off a $60 jacket is a $12 saving), a restaurant tip (18% of a $45 bill is $8.10), sales tax, commission, or interest for a single period. Because it works on any number, you can just as easily find 15% of 200 as 6.5% of 1,240.

The second mode, 'X is what percent of Y', turns two raw numbers into a proportion using X ÷ Y × 100, so 30 is what percent of 200 gives 30 ÷ 200 × 100 = 15%. Use it for a test score (42 out of 50 is 84%), a completion rate, a market share, how much of a budget you have spent, or any time you need to express one quantity as a share of a total. If the second number is zero the tool shows a clear error, because dividing by zero has no meaning.

The third mode, 'percentage change', measures growth or decline from a starting value to a new value with the formula (new − old) ÷ old × 100. A price that rises from 200 to 250 is a +25% increase, while a drop from 250 back to 200 is a −20% decrease — the two are not mirror images because each change is measured against its own starting point. A positive result is an increase, a negative result is a decrease, and equal values give 0%. This is the right mode for price rises, salary bumps, investment returns, traffic growth, weight loss, or any before-and-after comparison. If the starting value is zero the change is undefined and the tool says so instead of showing a misleading number.

Negative numbers are accepted wherever they make sense, results are rounded for a clean display while staying accurate to full precision so you never see floating-point noise like 30.000000000004, and the formula is echoed back every time so you can check the working or learn how it was done. Whether you are shopping for discounts, splitting a bill, grading a paper, tracking a metric, or doing homework, it gives exact percentage answers instead of guesswork.

Frequently asked questions

How do I calculate X percent of a number?
Use the 'X% of Y' mode, which applies the formula (X ÷ 100) × Y. For example, 15% of 200 is (15 ÷ 100) × 200 = 30, and 20% of 60 is 12. This is how you work out a discount, a tip, sales tax, or a commission on any amount.
How do I find what percentage one number is of another?
Use the 'X is what % of Y' mode, which divides the part by the whole and multiplies by 100: X ÷ Y × 100. So 30 is what percent of 200 gives 30 ÷ 200 × 100 = 15%, and a score of 42 out of 50 is 84%. The whole (the second number) cannot be zero.
How is percentage increase or decrease calculated?
Percentage change is (new − old) ÷ old × 100. Going from 200 to 250 is (250 − 200) ÷ 200 × 100 = +25% (an increase), while going from 250 to 200 is −20% (a decrease). A positive answer is growth, a negative answer is a decline, and equal values give 0%.
Why isn't 200 to 250 the same percentage as 250 to 200?
Because percentage change is always measured against the starting value, and the two changes have different starting points. From 200, a rise of 50 is 50 ÷ 200 = +25%. From 250, a fall of 50 is 50 ÷ 250 = −20%. The same 50-unit gap is a different share of a different base, so the percentages differ.
Can I use negative numbers, and what happens if I divide by zero?
Yes — negative numbers are accepted wherever they make sense, so −10% of 200 is −20 and a fall can produce a negative percentage change. Division by zero is guarded: if the whole is 0 in the 'what percent' mode, or the starting value is 0 in the '% change' mode, the tool shows a clear message instead of a misleading result.

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