I'm working in C# and need to divide a large decimal value while keeping four digits after the decimal point. Using decimal gives me the mathematically accurate result, but it contains an extra digit:
```csharp
decimal input = 964506164158.9453m;
decimal result = input / 2m;
Console.WriteLine(result); // 482253082079.47265
```
For my exercise, the expected result is `482253082079.4727`, so I need to round the quotient to four decimal places. What's the correct way to do that?
3 Answers
Use `Math.Round` and specify the number of decimal places:
```csharp
decimal input = 964506164158.9453m;
decimal result = Math.Round(input / 2m, 4, MidpointRounding.AwayFromZero);
Console.WriteLine(result); // 482253082079.4727
```
`decimal` is already preserving the exact value it can represent. The division produces `.47265`; rounding to four places changes that to `.4727`. `Math.Ceiling` is not the right tool here because it rounds the entire value upward rather than rounding at a selected decimal position.
Be careful if the number is coming from text rather than a C# decimal literal. A period or comma is interpreted according to the active culture. Parse it with the intended culture, for example:
```csharp
using System.Globalization;
decimal value = decimal.Parse(text, CultureInfo.InvariantCulture);
```
The `m` suffix in `964506164158.9453m` already makes the source-code literal a decimal; you don't need to replace the period with a comma there. Culture mainly matters when parsing or formatting strings.
The value you're seeing is not a precision failure. `964506164158.9453 / 2` is exactly `482253082079.47265`, so displaying `482253082079.4727` means applying a four-decimal-place rounding rule. You can also write it in two steps:
```csharp
decimal result = input / 2m;
result = Math.Round(result, 4);
```
If the requirement is simply four decimal places, `Math.Round(result, 4)` is enough. The `AwayFromZero` option only matters when the discarded digits are exactly at a midpoint, such as a value ending in `...5`.