Round half to even - unbiased rounding method used in finance
When exactly at .5, banker's rounding rounds to the nearest EVEN number
Banker's Rounding (Round Half to Even)
When a number is exactly halfway between two values, round to the nearest EVEN number
Standard Rounding
Always rounds .5 up - introduces bias
Banker's Rounding
Rounds .5 to even - eliminates bias
This method is called "banker's rounding" because it's commonly used in financial calculations to eliminate cumulative rounding bias. When rounding many numbers, standard rounding (always rounding .5 up) creates an upward bias. Banker's rounding eliminates this by rounding to even numbers, which distributes rounding errors more evenly.
Example 1: 2.5 → 2
Example 2: 3.5 → 4
Example 3: 2.6 → 3
Example 4: 2.4 → 2
| Original | Standard Rounding | Banker's Rounding |
|---|---|---|
| 0.5 | 1 | 0 (even) |
| 1.5 | 2 | 2 (even) |
| 2.5 | 3 | 2 (even) |
| 3.5 | 4 | 4 (even) |
| 4.5 | 5 | 4 (even) |
| 5.5 | 6 | 6 (even) |
Banker's rounding, also known as "round half to even" or "unbiased rounding," is a method designed to eliminate cumulative rounding bias in financial calculations. It's the default rounding method in many programming languages and financial systems.
Standard rounding (always rounding .5 up) creates a systematic upward bias. If you round many numbers that end in .5, you'll always round up, causing the sum to be higher than it should be. Banker's rounding solves this by rounding .5 to even numbers, which distributes the rounding equally between up and down.