Is there a simple function for rounding a DateTime down to the nearest 30 minutes, in C#?

Question

For example:

2011-08-11 16:59 becomes 2011-08-11 16:30

Answer 1

Here's how I handled it. Below is the base method and an overload to round to the nearest 30 minutes:

public static DateTime RoundMinutes(this DateTime value)
{
    return RoundMinutes(value, 30);
}

public static DateTime RoundMinutes(this DateTime value, int roundMinutes)
{
    DateTime result = new DateTime(value.Ticks);

    int minutes = value.Minute;
    int hour = value.Hour;
    int minuteMod = minutes % roundMinutes;

    if (minuteMod <= (roundMinutes / 2))
    {
        result = result.AddMinutes(-minuteMod);
    }
    else
    {
        result = result.AddMinutes(roundMinutes - minuteMod);
    }

    return result;
}