Truncate a DateTime in C#

Occasionally you need to truncate a date to the nearest year, month, day etc. E.g. you need to transform the date 2015-06-05 15:33:30 into 2015-06-05 00:00:00, i.e. truncate it to the nearest day and set the lower levels of the date to 0.

Here comes a series of extension methods to help you with that:

public static DateTime TruncateToYearStart(this DateTime dt)
{
    return new DateTime(dt.Year, 1, 1);
}
public static DateTime TruncateToMonthStart(this DateTime dt)
{
    return new DateTime(dt.Year, dt.Month, 1);
}
public static DateTime TruncateToDayStart(this DateTime dt)
{
    return new DateTime(dt.Year, dt.Month, dt.Day);
}
public static DateTime TruncateToHourStart(this DateTime dt)
{
    return new DateTime(dt.Year, dt.Month, dt.Day, dt.Hour, 0, 0);
}
public static DateTime TruncateToMinuteStart(this DateTime dt)
{
    return new DateTime(dt.Year, dt.Month, dt.Day, dt.Hour, dt.Minute, 0);
}
public static DateTime TruncateToSecondStart(this DateTime dt)
{
    return new DateTime(dt.Year, dt.Month, dt.Day, dt.Hour, dt.Minute, dt.Second);
}

You can call these functions directly on a date, e.g.:

DateTime truncated = DateTime.UtcNow.TruncateToHourStart();

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