Rounding Calculator

Standard rounding (half-up): if the digit after your rounding place is 5 or more, round up; if 4 or less, round down. Example: 3.145 rounded to 2 decimal places = 3.15 (since 5 ≥ 5, round up). 3.144 = 3.14 (since 4 < 5, round down).

Floor (round down): always rounds toward negative infinity. floor(3.9) = 3, floor(-3.1) = -4. Ceiling (round up): always rounds toward positive infinity. ceil(3.1) = 4, ceil(-3.9) = -3. Standard rounding (half-up) rounds 0.5 cases up: round(2.5) = 3, round(3.5) = 4.

Banker rounding rounds 0.5 cases to the nearest even digit: 2.5 → 2, 3.5 → 4, 4.5 → 4, 5.5 → 6. This reduces cumulative rounding bias when processing many numbers. Used in Python built-in round(), financial calculations, and IEEE 754 floating-point standard.

Divide by 5, round to nearest integer, multiply by 5. Example: round 17 to nearest 5: 17/5 = 3.4, round to 3, 3 x 5 = 15. Round 18: 18/5 = 3.6, round to 4, 4 x 5 = 20. Used in pricing (prices ending in 0 or 5) and practical measurements.

Floating-point numbers (how computers store decimals) cannot exactly represent most decimal fractions. 0.1 + 0.2 = 0.30000000000000004 in JavaScript. This is not a bug — it is how binary floating-point works. For financial calculations, use integer arithmetic (store cents, not dollars) or decimal libraries to avoid these issues.