Subtract one month from Datetime.Today

Question

I have a DateTimePicker in which I allow user to select month previous to the current year.

The problem is, that if the date is 1st January, it can\'t calc

Answer 1

Just substract a month by 'adding` -1:

var lastmonth = DateTime.Today.AddMonths(-1);

See the MSDN documentation on DateTime.AddMonths.

Answer 2

If you, like Adil H. Raza, don't like to have negative numbers in your code, you could also make an extension method:

public static DateTime SubtractMonths(this DateTime dt, int months) => dt.AddMonths(-months);

And use it like

var lastmonth = DateTime.Today.SubtractMonths(1);

Answer 3

Patrick got it. To build on his answer and improve error handling (if there's a possibility that qs could be an invalid date string), you might do something like:

DateTime qsValue;

dateTimePicker1.MaxDate = DateTime.Today.AddMonths(-1);

dateTimePicker1.Value = (DateTime.TryParse(qs, out qsValue))
    ? qsValue
    : dateTimePicker1.MaxDate;