datime-now-vs-utcnow

🌳 Sustainable Code - DateTimeOffset vs. DateTime 📊

Difference of DateTimeOffset vs. DateTime

The big lack of DateTime, which was also recognized early in .NET 1.0, is that it is not clear from the DateTime information which time zone the time information represents. Therefore DateTime is also called implicit representation of time information, whose "hope" is that the time information is always in relation to UTC-0. DateTime cannot guarantee this, which is why errors often occur in combination with time zones and DateTime.

Since the problems of DateTime were recognized early, there was a much better alternative in the form of DateTimeOffset, which has been the recommended variant since .NET 1.1. Probably because DateTime appears in IntelliSense earlier than DateTimeOffset, this is often used despite the massive deficits and the large error potential of DateTime.

Docs:

• DateTimeOffset.UtcNow
• DateTimeOffset.Now
• DateTime.UtcNow
• DateTime.Now

🔥 Benchmark

BenchmarkDotNet v0.13.9+228a464e8be6c580ad9408e98f18813f6407fb5a, Windows 10 (10.0.19045.3570/22H2/2022Update)
AMD Ryzen 9 5950X, 1 CPU, 32 logical and 16 physical cores
.NET SDK 8.0.100-rc.2.23502.2
  [Host]   : .NET 7.0.13 (7.0.1323.51816), X64 RyuJIT AVX2
  .NET 7.0 : .NET 7.0.13 (7.0.1323.51816), X64 RyuJIT AVX2
  .NET 8.0 : .NET 8.0.0 (8.0.23.47906), X64 RyuJIT AVX2


| Method                | Runtime  | Mean      | Error    | StdDev   | Ratio | RatioSD |
|---------------------- |--------- |----------:|---------:|---------:|------:|--------:|
| DateTimeOffset_UtcNow | .NET 7.0 |  29.25 ns | 0.256 ns | 0.227 ns |  1.00 |    0.00 |
| DateTimeOffset_Now    | .NET 7.0 |  97.67 ns | 1.710 ns | 1.600 ns |  3.35 |    0.07 |
| DateTime_UtcNow       | .NET 7.0 |  30.24 ns | 0.277 ns | 0.231 ns |  1.03 |    0.01 |
| DateTime_Now          | .NET 7.0 | 148.96 ns | 2.050 ns | 1.917 ns |  5.09 |    0.04 |
|                       |          |           |          |          |       |         |
| DateTimeOffset_UtcNow | .NET 8.0 |  23.90 ns | 0.025 ns | 0.019 ns |  1.00 |    0.00 |
| DateTimeOffset_Now    | .NET 8.0 |  72.49 ns | 1.222 ns | 1.143 ns |  3.04 |    0.05 |
| DateTime_UtcNow       | .NET 8.0 |  27.11 ns | 0.521 ns | 0.487 ns |  1.13 |    0.02 |
| DateTime_Now          | .NET 8.0 | 114.42 ns | 1.317 ns | 1.232 ns |  4.80 |    0.05 |

🏁 Results

• 🚀 UtcNow is way faster than Now, because no timezone allignment is necessary
• 🚀 DateTimeOffset is faster than DateTime
• All cases are faster in .NET 8

Remarks

• In an application, time information should always be treated as time zone neutral (i.e. UTC).
• The adjustment to the time zone should be done during the visualization of the time information (e.g. in the UI).
• The explicit way should always be preferred to an implicit one: therefore in .NET - whenever possible - DateTimeOffset should be used.

⌨️ Run this sample

dotnet run -c Release

Updates

• 2023/11 - Add .NET 8