Multiply Y by X and divide by 100. For example, 25% of 200 = (25 ÷ 100) × 200 = 50. Use mode 1 in the calculator to compute this directly.

How do I find what percent one number is of another?

Divide the part by the whole and multiply by 100. "30 is what percent of 150?" = (30 ÷ 150) × 100 = 20%. Use mode 2 in the calculator.

How do I calculate percentage change?

Subtract the old value from the new value, divide by the old value, and multiply by 100. A change from 80 to 100 = (100 − 80) ÷ 80 × 100 = +25%. A decrease gives a negative result.

Percentage Calculator

Part of Whole
Value	Maximum
50	200

Part of Whole

Value

Maximum

200

How to calculate percent change

Percent change measures how much a value has increased or decreased relative to its starting point. The formula is:

% change = (New − Old) ÷ Old × 100

A positive result is an increase; a negative result is a decrease. For example, a price that rises from $80 to $100 has increased by 25%: (100 − 80) ÷ 80 × 100 = 25. A price that drops from $100 to $80 has decreased by 20%: (80 − 100) ÷ 100 × 100 = −20.

Note that a 25% increase followed by a 20% decrease returns to the original value. Percent changes are not symmetric. This is why "percent change" and "percentage difference" are different things. Percentage difference treats both values equally and uses their average as the denominator.

Percentage formulas explained

All four calculator modes come from the same base relationship:

Part = (Percentage ÷ 100) × Whole

Rearranging gives the other three forms:

Find the part: Part = (X ÷ 100) × Y: used when you know the percentage and the whole.
Find the percentage: X% = (Part ÷ Whole) × 100: used when you have both values and want to express their ratio as a percentage.
Find the whole: Whole = Part ÷ (X ÷ 100): used when you know a partial amount and the percentage it represents.

Frequently asked questions

What is X% of Y?

Divide X by 100 to convert it to a decimal, then multiply by Y. For example, 15% of 240 = 0.15 × 240 = 36. Use mode 1 in the calculator to compute this quickly.

How do I calculate the percentage difference?

Percentage difference is symmetric and uses the average of the two values as the base: |A − B| ÷ ((A + B) ÷ 2) × 100. For example, the percentage difference between 80 and 100 = 20 ÷ 90 × 100 ≈ 22.2%. This differs from percent change, which uses only the starting value as the base.

Why does a 10% increase followed by a 10% decrease not return to the original?

Because the 10% decrease applies to the already-increased value. Starting at 100: +10% -> 110, then −10% -> 99. The base changed. To reverse a p% increase exactly, you need to decrease by p ÷ (1 + p/100) percent.

How do I calculate tip percentage?

Tip percentage is a "what is X% of Y?" problem. If the bill is $65 and you want to leave 18%, use mode 1: 18% of 65 = $11.70. The Tip Calculator tool on this site handles the full calculation including split between multiple people.

Common percentage mistakes

Confusing percent change with percentage points: if an interest rate rises from 2% to 3%, it has increased by 1 percentage point, but by 50% in relative terms. "Percent" always refers to a relative change unless "percentage points" is specified.
Applying successive discounts incorrectly: a 20% discount followed by a 10% discount is not a 30% discount. It equals 1 − (0.8 × 0.9) = 1 − 0.72 = 28% total discount.
Mixing up increase and decrease reversal: to reverse a 25% increase, you don't subtract 25%. You need to decrease by 20% (divide by 1.25). In general, to reverse an increase of p%, decrease by p/(1+p) × 100.

Percentage in everyday contexts

A few reference points that are useful to internalize:

1% of any number: move the decimal point 2 places left (1% of 450 = 4.50)
10%: move the decimal point 1 place left (10% of 450 = 45)
5%: half of 10% (5% of 450 = 22.50)
15%: add 10% and 5% (15% of 450 = 45 + 22.50 = 67.50)
20%: one-fifth; divide by 5 (20% of 450 = 90)
25%: one-quarter; divide by 4 (25% of 450 = 112.50)