C# Tip – Calculate the beginning and end of month for a date

When I write reports, usually some of them need to use a date range. For example, the user wants to include all their account transactions for the month.

Here are two extension methods I use to calculate the dates for the beginning and end of the month (down to the second).

using System;
namespace DotNetToolBox
{
    public static class DateTimeMethods
    {
        public static DateTime StartOfMonth(this DateTime date)
        {
            return new DateTime(date.Year, date.Month, 1, 0, 0, 0);
        }
        public static DateTime EndOfMonth(this DateTime date)
        {
            return date.StartOfMonth().AddMonths(1).AddSeconds(-1);
        }
    }
}

It’s simple to use them. Just do this, to get variables for the beginning and end of the current month:

DateTime today = DateTime.Now;
DateTime startOfMonth = today.StartOfMonth();
DateTime endOfMonth = today.EndOfMonth();

These are extremely useful methods to add to your “toolbox” library (which, every good developer should have).