Percentage Calculator

How to Use

Start by picking one of the three mode cards at the top: "What is X% of Y?", "X is what % of Y?", or "% Change from X to Y". Selecting a mode clears any previous numbers and updates the two input labels to match that calculation. For example, in the first mode the fields read "Percentage (%)" and "Number (Y)", in the second they read "Value (X)" and "Total (Y)", and in the third they read "From (X)" and "To (Y)". Type a number into each box (decimals and negatives are allowed), and the result card appears automatically beneath the inputs, with a percent sign added for the "is what %" and "% change" modes. There is no submit button to press and nothing to clear manually when you switch modes.

Why This Tool Is Useful

Percentages show up everywhere in daily life, from sale prices and restaurant tips to exam grades, interest rates, and data reports, and the rules differ just enough to trip people up. This calculator removes that friction by separating the three most common questions into distinct modes so you never apply the wrong formula. Because each mode renames its fields, you avoid the classic mistake of swapping the part and the whole. Non-integer answers are shown rounded to two decimal places for readability (whole-number answers display without decimals) while the underlying math uses full floating-point precision, so it is reliable for both quick estimates and careful work. And since it is browser-based, it is free, instant, and private.

How to Calculate the Percentage of Marks

To turn marks into a percentage, divide the marks you scored by the total marks possible and multiply by 100. If you scored 425 out of 500, that is (425 / 500) x 100 = 85%. This is exactly the calculation behind the tool's second mode, "X is what % of Y?", where X is the marks obtained and Y is the maximum marks.

Select that mode, enter your obtained marks in the Value (X) field and the total marks in the Total (Y) field, and the percentage appears instantly. The tool does not have a dedicated marks mode, but this is the standard marks-to-percentage formula and it gives the same answer.

• Marks percentage = (marks obtained / total marks) x 100
• Example: 68 out of 80 = (68 / 80) x 100 = 85%
• Use mode 2 ("X is what % of Y?") with X = your marks and Y = total marks

What Percent Is X of Y? Finding One Number as a Percentage of Another

"What percent is X of Y" is one of the most searched percentage questions, and it is the same operation as the marks calculation: you are expressing a part as a percentage of a whole. The formula is (X / Y) x 100, where X is the part and Y is the whole or total.

If 18 people out of a group of 40 chose option A, then 18 is (18 / 40) x 100 = 45% of the group. In the tool, choose "X is what % of Y?", put the part in the Value (X) field and the total in the Total (Y) field. Keeping the part and the total in the right boxes is the only thing you need to get right, and the relabeled fields make that easy.

How to Calculate a Percentage Increase or Decrease

A percentage increase or decrease measures how much a value has gone up or down relative to where it started. The tool's third mode, "% Change from X to Y", computes this as ((Y - X) / |X|) x 100, where X is the original (From) value and Y is the new (To) value.

A positive result means an increase and a negative result means a decrease. For instance, a price rising from 80 to 100 gives ((100 - 80) / 80) x 100 = +25%, while a price falling from 100 to 80 gives ((80 - 100) / 100) x 100 = -20%. Note that the increase and decrease percentages are not symmetric, because each is measured against its own starting value.

• Percentage increase: new value higher than original gives a positive result
• Percentage decrease: new value lower than original gives a negative result
• Formula: ((To - From) / |From|) x 100
• Going up 25% then down 20% returns you to the start, not the same percentage

Percentage Change vs Percentage Difference: What's the Difference?

These two terms are constantly confused, but they answer different questions. Percentage change is directional and is measured relative to the original value: it tells you how much a number grew or shrank from a known starting point. Its formula is ((new - old) / |old|) x 100, and this is what the tool's "% Change" mode calculates.

Percentage difference, by contrast, has no "before" and "after". It compares two values where neither is the reference point, so it is measured relative to the average of the two. Its formula is (|A - B| / ((A + B) / 2)) x 100. Use percentage change when one value clearly came first (last year's revenue versus this year's). Use percentage difference when comparing two independent measurements (two lab readings, two store prices) where neither is the baseline.

Worth knowing: this tool computes percentage change, not percentage difference. To find the percentage difference between two values, apply the average-based formula above by hand. As a quick example, comparing 40 and 60: the percentage difference is (|40 - 60| / 50) x 100 = 40%, whereas the percentage change from 40 to 60 is +50% and from 60 to 40 is -33.33%.

• Percentage change: relative to the ORIGINAL value, has a direction (+/-)
• Percentage difference: relative to the AVERAGE of the two values, always positive
• Change formula: ((new - old) / |old|) x 100
• Difference formula: (|A - B| / ((A + B) / 2)) x 100

How to Find an Overall Percentage Across Multiple Subjects

When you need a single overall percentage from several subjects, do not average the individual subject percentages unless every subject is out of the same total. The reliable method is to add up all the marks you obtained, add up all the maximum marks, and then express the first total as a percentage of the second.

For example, if you scored 78/100, 65/100, and 90/100, your total is 233 out of 300, giving (233 / 300) x 100 = 77.67%. Enter 233 as X and 300 as Y in the "X is what % of Y?" mode to confirm it. This sum-of-marks approach automatically weights each subject by its maximum and avoids the rounding errors of averaging percentages.

How Percentage Math Works Behind the Scenes

Every percentage problem reduces to one idea: a percentage is just a fraction out of 100. "Per cent" literally means "per hundred", so 50% is 50/100 = 0.5. To find a percentage of a number, convert the percent to a decimal and multiply, which is exactly what the first mode does: (X / 100) x Y.

Once you internalize this, all three modes are variations on rearranging the same equation. Finding what percent X is of Y solves for the percentage instead of the part, and percentage change applies the same fraction to the difference between two numbers. The fraction-to-percent table below makes the most common conversions instant.

Fraction-to-Percent Quick Reference