JavaScript Math Reference

Basic Rounding Functions

Math.floor(x) -> Always rounds DOWN to nearest integer

Math.floor(4.9); // 4
Math.floor(4.1); // 4
Math.floor(-4.1); // -5 (down means more negative)
Math.floor(-4.9); // -5

Math.ceil(x) -> Always rounds UP to nearest integer

Math.ceil(4.1); // 5
Math.ceil(4.9); // 5
Math.ceil(-4.9); // -4 (up means less negative)
Math.ceil(-4.1); // -4

Math.round(x) -> Rounds to nearest integer (0.5 rounds up)

Math.round(4.4); // 4
Math.round(4.5); // 5
Math.round(4.6); // 5
Math.round(-4.5); // -4
Math.round(-4.6); // -5

Math.trunc(x) -> Removes decimal part (truncates toward zero)

Math.trunc(4.9); // 4
Math.trunc(4.1); // 4
Math.trunc(-4.9); // -4 (toward zero)
Math.trunc(-4.1); // -4

Rounding to Decimal Places

Round to N decimal places:

// Round to 2 decimal places
Math.round(4.567 * 100) / 100; // 4.57
Number((4.567).toFixed(2)); // 4.57

// Round to 1 decimal place
Math.round(4.567 * 10) / 10; // 4.6

Quick Reference

Function	4.2	4.7	-4.2	-4.7
`floor`	4	4	-5	-5
`ceil`	5	5	-4	-4
`round`	4	5	-4	-5
`trunc`	4	4	-4	-4

Memory trick: Floor goes down, ceiling goes up, truncate cuts off decimals, round goes to nearest.

JavaScript Math Reference

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Basic Rounding Functions

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Quick Reference

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Basic Rounding Functions

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Quick Reference