The calc() function lets you perform basic math operations on values, and it’s especially useful when you need to add or subtract a length value from a percentage.

This is how it works:

div {
	max-width: calc(80% - 100px)
}

It returns a length value, so it can be used anywhere you expect a pixel value.

You can perform

• additions using +
• subtractions using -
• multiplication using *
• division using /

One caveat: with addition and subtraction, the space around the operator is mandatory, otherwise it does not work as expected.

Examples:

div {
	max-width: calc(50% / 3)
}

div {
	max-width: calc(50% + 3px)
}