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Percentage Calculator

Three everyday percentage problems, solved instantly: what is X% of Y, X is what percent of Y, and the percentage change from one value to another. Discounts, tips, taxes, test scores and price rises — this is the math daily life keeps asking for.

1) What is X% of Y?

Percent (%)

Of number

2) X is what percent of Y?

Number (X)

Of number (Y)

3) Percentage change from X to Y

From (old value)

To (new value)

The Three Questions Behind Almost Every Percentage

Strip away the context and nearly every real-world percentage problem is one of three questions. "What is X% of Y?" — a 20% discount on an $85 jacket, a 15% tip on a $64 dinner, 8% sales tax. "X is what percent of Y?" — you scored 43 of 50 on a test, your team won 31 of 82 games, a task is 17 of 20 steps done. "What's the percentage change from X to Y?" — rent went from $1,200 to $1,320, a stock moved from $48 to $42, your salary rose from $52,000 to $55,900. This page puts all three side by side, because in practice people constantly mix them up — especially the second and third.

Percentages feel slippery because they're relative: the same $10 is 50% of $20 and 1% of $1,000. They also hide a famous trap — percentages don't cancel out symmetrically. A price that rises 20% then falls 20% doesn't return to where it started, and this calculator is the quickest way to prove that to yourself (try it: 100 up 20% is 120; 120 down 20% is 96).

How to Use the Percentage Calculator

Find the section matching your question — the three calculators are numbered and labeled in plain language.
Enter your two numbers. Decimals are fine: 7.5% tax and 12.75 prices work exactly as you'd expect.
Read the result as you type. There's no equals button to hunt for.
Sanity-check big answers with a rough estimate — 10% is easy to find (just move the decimal), and most percentages are near a multiple of it.

A Worked Example for Each Question

Discount: What is 30% off $129.99? The first calculator says 30% of 129.99 is 39.00 — so you pay $129.99 − $39.00 = $90.99.

Score: You answered 37 of 45 questions correctly. The second calculator: 37 is 82.2% of 45 — a solid B in most grading schemes.

Change: Your monthly grocery spend went from $640 to $736. The third calculator reports a 15% increase — (736 − 640) ÷ 640 × 100. Whether that's inflation or lifestyle creep, at least now it's a number you can act on.

Tips for Not Getting Fooled by Percentages

"Percent of" vs "percentage points" are different. An interest rate rising from 4% to 5% is up 1 percentage point — but a 25% relative increase. News headlines exploit the confusion constantly.
Anchor with 10%. To estimate any percentage mentally: find 10% (move the decimal one place), then scale — 30% is three times that, 5% is half of it.
Successive changes multiply, they don't add. A 10% raise followed by a 10% raise is a 21% total increase, not 20% — each applies to a bigger base.
Always ask "percent of what?" "50% more" is meaningless until the base is named. It's the oldest trick in advertising.

Common Mistakes to Avoid

Reversing the change formula. Percentage change is always (new − old) ÷ old. Dividing by the new value instead gives a different, wrong answer — and the error grows with bigger changes.
Believing up-then-down returns to zero. Up 50% then down 50% leaves you 25% below the start. The down percentage acts on the inflated value.
Adding percentages of different bases. "20% off, then another 10% off" is 28% off total, not 30% — the second discount applies to the already-reduced price.
Confusing a discount with the price paid. 30% off $100 is a $30 discount and a $70 payment. Reading the calculator's "30% of" result as the final price is the classic checkout error.

Frequently Asked Questions

How do I calculate a percentage of a number?

Multiply the number by the percentage divided by 100. For example, 15% of 240 = 240 × 0.15 = 36. The first calculator on this page does it instantly, including decimals.

What's the difference between percentage change and percentage difference?

Percentage change compares an old value to a new one over time and has a direction — up or down. It always divides by the old value. (Percentage difference, used when neither value is “first”, divides by the average instead — this page's third tool is the everyday change version.)

How do I turn a fraction or score into a percentage?

Divide the part by the whole and multiply by 100 — that's the second calculator. 37 ÷ 45 = 0.822, which is 82.2%.

Why doesn't a 20% rise followed by a 20% fall get me back to the start?

Because the two percentages act on different amounts. 100 rising 20% becomes 120; 20% of 120 is 24, so falling 20% lands at 96. The bases differ, so the amounts differ.

How do I calculate a tip or tax quickly?

For a tip, use the first calculator: 18% of a $64 bill is $11.52. For tax, calculate the percentage of the pre-tax price and add it on — or multiply the price by 1 plus the rate (× 1.08 for 8%).

Can the calculator handle decimals and negative changes?

Yes. Enter rates like 7.5% and values of any size. For the change calculator, if the new value is smaller, the result shows as a negative percentage — a decrease.