How to calculate difference between two dates (number of days) in C#?

The simplest and most common way to find the difference in days between two dates in C# is to subtract one DateTime from another and then work with the resulting TimeSpan.

Using Subtraction and TimeSpan.Days

DateTime startDate = new DateTime(2024, 1, 1);
DateTime endDate = new DateTime(2024, 1, 15);

// Subtract startDate from endDate
TimeSpan difference = endDate - startDate;

// Get the difference in whole days
int totalDays = difference.Days;  // 14
Console.WriteLine(totalDays);

• Key Point: difference.Days returns the integer number of days (truncating any partial days). If you need fractional days (e.g., 14.5 days), use difference.TotalDays, which returns a double.

Handling Edge Cases

1. Time Components: If the DateTime objects also contain time information, subtracting will include hours, minutes, and seconds. Using difference.Days drops the fractional part.
2. DateTimeKind: Make sure both DateTime objects are in the same “kind” (e.g., both are Utc or both are Local). Mixing different DateTimeKind values can cause subtle errors.
3. DateTimeOffset: If you’re dealing with offsets or different time zones, consider using DateTimeOffset for more accurate calculations.

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