How Precise is C#'s DateTime.Now, and When Should I Use Stopwatch Instead?

C# DateTime.Now: Accuracy and Granularity Explained

The common C# method DateTime.UtcNow for retrieving the current date and time has shown unexpected behavior in recent unit tests. Repeated calls in quick succession sometimes return identical values, prompting questions about its precision.

Precision vs. Accuracy

It's important to differentiate between precision and accuracy. A precise measurement consistently yields the same result when repeated, whereas accuracy reflects how close the measurement is to the true value. DateTime.Now prioritizes precision over high accuracy, as it lacks access to reliable, high-precision time sources.

The Role of DateTime

DateTime serves a specific purpose: representing and manipulating dates and times. It's excellent for displaying the current time, calculating time intervals, and similar tasks.

Performance Trade-offs

The design of DateTime prioritizes performance over microsecond precision. Providing such granularity would be misleading given the lack of universally available microsecond-accurate time sources.

Stopwatch: The Precision Solution

For applications requiring highly precise timing, Stopwatch is the preferred tool. It's specifically designed to measure elapsed time intervals with greater accuracy and finer granularity.

Summary

DateTime.Now's precision limitations arise from its focus on date and time representation, not precise time measurement. For scenarios demanding accurate and precise timing, Stopwatch offers a superior solution.

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