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Percentage Calculator

Instant math tool for students, finance managers, shoppers, and researchers. Solve X% of Y, percentage increase/decrease, and percentage difference instantly.

What is X% of Y?

%
Quick Presets:
Answer
30

15% of 200 is equal to 30

Original Value
200
Percentage
15%
Remaining
170
Calculation Step:
(15 ÷ 100) × 200 = 0.1500 × 200 = 30

Percentages are simple arithmetic that almost everyone gets wrong under time pressure, usually by confusing 'percent of' with 'percent change' or by reversing the base. This calculator handles the four questions people actually ask — what is X% of Y, X is what percent of Y, what is the change from X to Y, and what number is X% of — and shows the working so you can check it rather than trust it.

Formulas & Mathematical Logic

Percentage of a Number

Formula 1
P = (X / 100) × Y

Divide percentage by 100 and multiply by the total value.

Example: 15% of 200 = (15 / 100) * 200 = 30.

How to calculate a percentage

  1. Pick the calculation type that matches your question. 'Percent of' answers 'what is 15% of 240'; 'percent change' answers 'sales went from 240 to 300, by how much did they grow'.
  2. Enter your two numbers. The labels update to tell you which value belongs in which field.
  3. Read the result along with the formula breakdown shown underneath.
  4. For percent change, check the sign: a negative result is a decrease, a positive result is an increase.

The Percentage Calculator runs entirely in your browser — nothing you enter is uploaded, stored, or logged.

When to use this tool

Working out a tip or a service charge

A 15% tip on a 1,240 bill is 186, for a total of 1,426. Using 'percent of' gives the tip alone; adding it to the bill gives what you actually pay.

Measuring growth between two periods

If revenue moved from 84,000 to 97,000, percent change gives +15.48%. This is the number to quote in a report — the absolute difference of 13,000 means little without the base.

Reverse-engineering a total from a part

If 45 students represent 18% of a cohort, the full cohort is 250. This is the calculation people most often get backwards, because the instinct is to multiply rather than divide.

Things worth knowing

  • A percentage increase followed by the same percentage decrease does not return you to the start: +20% then −20% leaves you 4% down.
  • Percentage points and percent are different. A rate moving from 4% to 6% is a rise of 2 percentage points, but a 50% increase.
  • To add X% to a number in one step, multiply by (1 + X/100). To remove it, divide by (1 + X/100) — do not subtract X%.

Frequently Asked Questions

How to calculate percent mentally?

Find 10% by shifting the decimal left, then scale accordingly.

How do I calculate percentage change between two numbers?

Subtract the old value from the new value, divide by the old value, then multiply by 100. Going from 240 to 300: (300 − 240) ÷ 240 × 100 = 25%. The old value is always the denominator — using the new value is the single most common error.

How do I remove a percentage that has already been added?

Divide rather than subtract. If a price of 118 already includes 18% tax, the pre-tax price is 118 ÷ 1.18 = 100, not 118 − 18% = 96.76. Subtracting applies the percentage to the wrong base.

What does it mean when a percentage is over 100%?

It simply means the part is larger than the base. Growing from 40 to 100 is a 150% increase. Values over 100% are perfectly valid for change and ratio calculations, though not for a share of a whole.

How do I calculate a percentage in reverse?

If you know the result and the percentage, divide the result by the percentage expressed as a decimal. 45 being 18% of an unknown total gives 45 ÷ 0.18 = 250.

Why do two successive discounts not add up?

Because the second discount applies to the already-reduced price. A 20% discount followed by a 10% discount is a total reduction of 28%, not 30%, since 0.8 × 0.9 = 0.72.

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