ToolNest

Percentage Calculator

All common percentage calculations in one place: percent of a number, percentage change, ratio to percentage and increase/decrease.

Number A
Number B

The four calculations people actually need

1. What is X% of Y?

result = Y x (X / 100)

A 15% tip on an $80 meal is $12.

2. What percentage is X of Y?

result = (X / Y) x 100

$12 is 15% of $80.

3. Percentage change

result = ((new - old) / old) x 100

Always divide by the original value, not the new one. Dividing by the new value gives a different, wrong number — a common mistake in reporting.

4. Increase or decrease by X%

result = Y x (1 + X/100)

A price of $80 increased by 15% is $92, not $95. The 15% applies to the original.

A note on the classic "20% increase then 20% decrease" trap

These do not cancel out. A $100 price increased by 20% becomes $120. Decreasing that by 20% gives $96, not $100. You need a 16.67% decrease to return to the original. This matters when reading compounding claims in marketing copy.

Percentage points vs percent

These are different and often confused:

  • Percentage points — the raw difference between two percentages. Interest going from 4% to 6% is a rise of 2 percentage points.
  • Percent change — the relative change. Interest going from 4% to 6% is a rise of 50%.

Related

Working with dimensions instead? The length converter handles every CSS unit.

Frequently asked questions

What is X% of Y?

Multiply Y by X and divide by 100. A 15% tip on an $80 meal is $12.

How do I calculate a percentage change?

Subtract the old value from the new one, divide by the old value, then multiply by 100. Always divide by the original, never the new value.

Why does a 20% increase then a 20% decrease not return to the original?

Because the percentages apply to different bases. $100 rises 20% to $120, and 20% of $120 is $24, so it falls to $96. A 16.67% decrease would restore $100.

What is the difference between percentage points and percent change?

Percentage points is the raw gap between two percentages. Interest going from 4% to 6% is 2 percentage points but a 50% change.

Which numbers can I enter?

Decimals are fine. The calculator rounds to six decimal places, which is more precision than any percentage calculation meaningfully carries.