DateTime.AddMonths question

Question

Hello,

lets say, I have 28th of February 2010 and add one months to this date using AddMonths(1)...the resulting date is 28th of March, but not 31st of March, which I want. Is there a way to tweak that a bit so this works without adding custom code?

Edit: I dont need the last day of a month, actually I need to add one month, but when its the last day of a month, I need to find the last day of the next month.

Thanks!

Answer 1

No - it doesn't take that into account. It's custom code all the way!

Will your code only be interested in the last day of months, or do you want code to add a month to any date, but take into account when the date supplied is the last day of the month?

Answer 2

Try overloading the day property and setting it to 32. Whgen this is done in JavaScript, I believe it defaults back to the last day of whatever month you're in.

Answer 3

I don't know what you want to achieve, but you could add one day, add a month and subtract one day.

DateTime nextMonth = date.AddDays(1).AddMonths(1).AddDays(-1);

EDIT:

As one of the commenters points out, this sometimes gives the wrong result. After reading your updated question, I think the easiest way of calculating the date you want is:

public static DateTime NextMonth(this DateTime date)
{
   if (date.Day != DateTime.DaysInMonth(date.Year, date.Month))
      return date.AddMonths(1);
   else 
      return date.AddDays(1).AddMonths(1).AddDays(-1);
}

This extension method returns next month's date. When the current date is the last day of the month, it will return the last day of next month.

Answer 4

If you mean that the resultant date should be the same distance from the end of the month, then you're into custom code - something like (not fully tested, especially re 28/30/31 months):

class Program
{
    static void Main()
    {
        var when = DateTime.Today;
        DateTime fromEndOfNextMonth = when.AddMonthsRelativeToEndOfMonth(1);
    }

}
public static class DateTimeExtensions
{
    public static DateTime AddMonthsRelativeToEndOfMonth(
               this DateTime when, int months)
    {
        if (months == 0) return when;
        DateTime startOfNextMonth = when;
        int month = when.Month;
        while (startOfNextMonth.Month == month)
        {
            startOfNextMonth = startOfNextMonth.AddDays(1);
        }
        TimeSpan delta = startOfNextMonth - when;
        return startOfNextMonth.AddMonths(1) - delta;
    }

}

Answer 5

I solved it now, by checking if it is the last day of a month using GetLastDayInCurrentMonth. If thats the case, I use

DateTime nextMonth = date.AddDays(1).AddMonths(1).AddDays(-1);

If its not the last day, I just use AddMonths(1)

Thanks guys!

Answer 6

if(yourDate.Day == DaysInMonth(yourDate.Year,yourDate.Month)) //check for last day
    yourDate.AddDays(DateTime.DaysInMonth(yourDate.Year,(yourDate.Month+1)%12));

Answer 7

public static class DateTimeExtensions
{
    public static DateTime AddMonthsCustom(this DateTime source, int months)
    {
        DateTime result = source.AddMonths(months);
        if (source.Day != DateTime.DaysInMonth(source.Year, source.Month))
            return result;

        return new DateTime(result.Year, result.Month,
                            DateTime.DaysInMonth(result.Year, result.Month),
                            result.Hour, result.Minute, result.Second,
                            result.Millisecond, result.Kind);
    }
}