Percentage Calculator

Part of Whole
Value	Maximum
50	200

How to use this tool

Choose a mode. Select one of the six calculation modes: solve a part, rate, whole, directional percent change, signed percentage adjustment, or symmetric percentage difference.
Enter your numbers. Fill in the two input fields. Labels update automatically to describe what each number represents in the selected mode.
Read the result. The answer updates instantly below the inputs. Switching modes keeps your current values while changing their labels and meaning. Select Load example values to restore the active mode’s sample numbers.

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

The three part-and-whole 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.

The signed adjustment mode calculates a new value with Starting value × (1 + Percent ÷ 100); enter a negative percentage for a decrease. The symmetric difference mode divides the absolute gap between two non-negative values by their average, then multiplies by 100. It requires a nonzero average, while percent change instead uses the signed starting value as its denominator.

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)

Frequently asked questions

What is X% of Y?

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 signed old value, and multiply by 100. A change from 80 to 100 = (100 − 80) ÷ 80 × 100 = +25%. A decrease gives a negative result. With a negative starting value, the signed denominator can make the direction less intuitive.

How do I calculate the percentage difference?

Choose Difference (%) mode to calculate |A − B| ÷ ((A + B) ÷ 2) × 100. It treats both values equally and requires non-negative values with a nonzero average. Percentage change (mode 4) is directional - it compares a new value to a specific baseline.

How do I increase or decrease a value by a percentage?

Choose X ± P% and enter a starting value with a signed percentage. A positive percentage increases the value and a negative percentage decreases it. For example, 100 adjusted by −10% gives 90; the result also shows the change amount.

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.