files/en-us/web/css/reference/values/mod/index.md
The mod() CSS function returns a modulus left over when the first parameter is divided by the second parameter, similar to the JavaScript remainder operator (%). The modulus is the value left over when one operand, the dividend, is divided by a second operand, the divisor. It always takes the sign of the divisor.
The calculation is a - (Math.floor(a / b) * b). For example, the CSS mod(21, -4) function returns the remainder of -3. The full calculation is 21 - (Math.floor(21 / -4) * -4). When dividing 21 by -4, the result is -5.25. This is floored to -6. Multiplying -6 by -4 is 24. Subtracting this 24 from the original 21, the remainder is -3.
/* Unitless <number> */
line-height: mod(7, 2); /* 1 */
line-height: mod(14, 5); /* 4 */
line-height: mod(3.5, 2); /* 1.5 */
/* Unit based <percentage> and <dimension> */
margin: mod(15%, 2%); /* 1% */
margin: mod(18px, 4px); /* 2px */
margin: mod(19rem, 5rem); /* 4rem */
margin: mod(29vmin, 6vmin); /* 5vmin */
margin: mod(1000px, 29rem); /* 72px - if root font-size is 16px */
/* Negative/positive values */
rotate: mod(100deg, 30deg); /* 10deg */
rotate: mod(135deg, -90deg); /* -45deg */
rotate: mod(-70deg, 20deg); /* 10deg */
rotate: mod(-70deg, -15deg); /* -10deg */
/* Calculations */
scale: mod(10 * 2, 1.7); /* 1.3 */
rotate: mod(10turn, 18turn / 3); /* 4turn */
transition-duration: mod(20s / 2, 3000ms * 2); /* 4s */
The mod(dividend, divisor) function accepts two comma-separated values as its parameters. Both parameters must have the same type, number, dimension, or {{cssxref("percentage")}}, for the function to be valid. While the units in the two parameters don't need to be the same, they do need of the same dimension type, such as {{cssxref("length")}}, {{cssxref("angle")}}, {{cssxref("time")}}, or {{cssxref("frequency")}} to be valid.
dividend
divisor
Returns a {{CSSxREF("<number>")}}, {{CSSxREF("<dimension>")}}, or {{CSSxREF("<percentage>")}} (corresponds to the parameters' type) representing the modulus, that is, the operation left over.
divisor is 0, the result is NaN.dividend is infinite, the result is NaN.divisor is positive the result is positive (0⁺), and if divisor is negative the result is negative (0⁻).{{CSSSyntax}}
{{Specifications}}
{{Compat}}