MATH · ROUNDING
Rounding Calculator
Round any number to a specified number of decimal places using half-up (standard) or half-even (banker's) rounding. Supports negative decimal places.
About This Calculator
Rounding reduces the precision of a number to a specified level. Standard half-up rounding (what most people learned in school) rounds 2.5 to 3. Banker's rounding (half-even) rounds 2.5 to 2 and 3.5 to 4 — always rounding to the nearest even digit at the midpoint, which reduces cumulative rounding bias in large datasets.
How It Works
Enter the value, choose the number of decimal places (negative values round to the left of the decimal point — e.g. −2 rounds to the nearest hundred), and select the rounding mode. Half-up uses JavaScript's standard Math.round. Half-even uses a custom implementation because JavaScript's Math.round does not support banker's rounding natively.
The Formula
Half-up: floor(x × 10^d + 0.5) / 10^d Half-even: round to nearest even at midpoint
- d
- decimal places (positive = right of decimal, negative = left)
Frequently Asked Questions
- Why would I use banker's rounding?
- Standard half-up rounding biases the average upward when many values end in exactly 0.5. Banker's rounding (half-even) eliminates this bias by rounding up as often as down at the midpoint. It is the default in many scientific, financial, and statistical computing environments including Python's built-in round() and IEEE 754 arithmetic.
- What do negative decimal places mean?
- Negative decimal places round to the left of the decimal point. −1 rounds to the nearest ten, −2 to the nearest hundred, and so on. Useful for presenting large numbers with reduced precision: rounding 12345 to −2 gives 12300.
- Is this the same as truncation?
- No. Truncation simply removes digits without rounding — 2.9 truncated to 0 decimal places is 2. Both modes here round to the nearest value, not toward zero.