What three calculations does this tool handle?

Row one finds X% of a number ((X ÷ 100) × Y), row two expresses one number as a percentage of another ((X ÷ Y) × 100), and row three measures the percentage change between an old and a new value (((new − old) ÷ old) × 100). The rows are independent, so you can use any one of them without touching the others.

How do I calculate a discount or sale price?

Use the first row to get the discount amount, then subtract it from the price. For example, 25% of $80 is $20, so the sale price is $60. For a markup or a tip, add the result to the base amount instead of subtracting it.

What’s the difference between percentage change and percentage points?

Percentage change is relative to the starting value, while percentage points are the simple difference between two percentages. If an interest rate moves from 10% to 12%, that is a rise of 2 percentage points but a 20% relative increase. Mixing the two up is one of the most common statistics mistakes.

Why is my percentage change negative?

A negative result means the value decreased: going from 150 to 120 is a change of −20%. Note the asymmetry — climbing back from 120 to 150 is +25%, because the change is always measured against the starting value, which is smaller on the way back up.

What happens if I enter zero?

Taking a percent of zero works normally (any percent of 0 is 0). But asking what percent a number is of 0, or the change starting from 0, is mathematically undefined; in those cases the tool shows 0 rather than an error, so double-check that your base value is what you intended.

How are the results rounded?

The display rounds to at most two decimal places; the underlying math runs at full floating-point precision. When working with money, round only the final figure, not intermediate values, to avoid accumulating rounding errors.

Is my input uploaded?

No — all three calculations run in JavaScript in your browser, and nothing you type is sent to a server.

Percentage Calculator

Work out percentages: X% of Y, what percent one number is of another, and percentage change.

Runs in your browser — files never leave your device

What is% of = 30

is what % of = 15%

% change from to = 50%

How it works

This calculator answers the three percentage questions that come up most often in daily life: finding a percentage of a number (discounts, tips, commissions), expressing one number as a percentage of another (test scores, budget shares, market share), and measuring the percentage change between two values (price rises, weight loss, portfolio returns). Each row works independently and recalculates the moment you type, so it behaves like a scratch pad rather than a form you submit.

The three formulas, in the order the rows appear:

X% of Y = (X ÷ 100) × Y
X as a percentage of Y = (X ÷ Y) × 100
Percentage change from X to Y = ((Y − X) ÷ X) × 100

A fully worked example for the first row: what is 20% of 150? Divide the percentage by 100 to get a decimal factor (20 ÷ 100 = 0.2), then multiply: 0.2 × 150 = 30. In shopping terms, a $150 jacket with a 20% discount is reduced by $30, so you pay $120. The second row runs the same logic in reverse: to check what percent 30 is of 200, compute (30 ÷ 200) × 100 = 15%.

Percentage change trips people up because it is always measured relative to the starting value. Going from 80 to 92 is a +15% increase, but going back from 92 to 80 is a −13.04% decrease — the direction changes the base, so the magnitudes differ. For the same reason, a 20% drop from 150 to 120 needs a 25% gain to recover. A positive result means an increase and a negative result a decrease.

Results are shown rounded to two decimal places while the internal math keeps full precision. If the base of a “percent of what” or “change” calculation is zero, the answer is mathematically undefined and the tool displays 0 instead of an error.

Frequently asked questions

What three calculations does this tool handle?: Row one finds X% of a number ((X ÷ 100) × Y), row two expresses one number as a percentage of another ((X ÷ Y) × 100), and row three measures the percentage change between an old and a new value (((new − old) ÷ old) × 100). The rows are independent, so you can use any one of them without touching the others.
How do I calculate a discount or sale price?: Use the first row to get the discount amount, then subtract it from the price. For example, 25% of $80 is $20, so the sale price is $60. For a markup or a tip, add the result to the base amount instead of subtracting it.
What’s the difference between percentage change and percentage points?: Percentage change is relative to the starting value, while percentage points are the simple difference between two percentages. If an interest rate moves from 10% to 12%, that is a rise of 2 percentage points but a 20% relative increase. Mixing the two up is one of the most common statistics mistakes.
Why is my percentage change negative?: A negative result means the value decreased: going from 150 to 120 is a change of −20%. Note the asymmetry — climbing back from 120 to 150 is +25%, because the change is always measured against the starting value, which is smaller on the way back up.
What happens if I enter zero?: Taking a percent of zero works normally (any percent of 0 is 0). But asking what percent a number is of 0, or the change starting from 0, is mathematically undefined; in those cases the tool shows 0 rather than an error, so double-check that your base value is what you intended.
How are the results rounded?: The display rounds to at most two decimal places; the underlying math runs at full floating-point precision. When working with money, round only the final figure, not intermediate values, to avoid accumulating rounding errors.
Is my input uploaded?: No — all three calculations run in JavaScript in your browser, and nothing you type is sent to a server.

Percentage Calculator

How it works

Frequently asked questions

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