Get the previous month's first and last day dates in c#

Question

I can't think of an easy one or two liner that would get the previous months first day and last day.

I am LINQ-ifying a survey web app, and they squeezed a new requirement in.

The survey must include all of the service requests for the previous month. So if it is April 15th, I need all of Marches request ids.

var RequestIds = (from r in rdc.request 
                  where r.dteCreated >= LastMonthsFirstDate && 
                  r.dteCreated <= LastMonthsLastDate 
                  select r.intRequestId);

I just can't think of the dates easily without a switch. Unless I'm blind and overlooking an internal method of doing it.

andleer · Accepted Answer · 2013-09-05T17:51:22.377

355

var today = DateTime.Today;
var month = new DateTime(today.Year, today.Month, 1);       
var first = month.AddMonths(-1);
var last = month.AddDays(-1);

In-line them if you really need one or two lines.

edited Sep 05 '13 at 17:51

answered Feb 26 '09 at 18:26

andleer

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IIRC DateTime.Today is a quite expensive call, so you better store the value in a variable first. Good answer anyway :) – Leandro López Feb 26 '09 at 19:26
2

@andleer here's a nice library which works like you mentioned http://fluentdatetime.codeplex.com/ – Matthew Lock Jun 01 '12 at 01:31
@MatthewLock, the link seems to be broken. – Guillermo Gutiérrez Feb 13 '13 at 20:46
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@guillegr123 now at github https://github.com/FluentDateTime/FluentDateTime and Nuget http://nuget.org/packages/FluentDateTime – Matthew Lock Feb 13 '13 at 23:32
2

I would just like to point out that if entries are stored using a a full datetime this query may fail to retrieve any that start after 12:00 AM on the last day of the month. You could solve this by changing the last line to read var last = month.AddTicks(-1); – SixOThree Dec 22 '14 at 22:12

MikeW · Answer 2 · 2009-02-26T20:19:12.823

29

The way I've done this in the past is first get the first day of this month

dFirstDayOfThisMonth = DateTime.Today.AddDays( - ( DateTime.Today.Day - 1 ) );

Then subtract a day to get end of last month

dLastDayOfLastMonth = dFirstDayOfThisMonth.AddDays (-1);

Then subtract a month to get first day of previous month

dFirstDayOfLastMonth = dFirstDayOfThisMonth.AddMonths(-1);

edited Feb 26 '09 at 20:19

answered Feb 26 '09 at 18:17

MikeW

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+1, but to be pedantic, you're better evaluating DateTime.Today once and storing in a local variable. If your code starts executing a nanosecond before midnight, two consecutive calls to DateTime.Today could return different values. – Joe Feb 26 '09 at 18:36
Yes, thanks, all of you correct, even the pedantic one Fixed the error. – MikeW Feb 26 '09 at 19:24
well let the compiler be less pedantic to you :) – Maksym Gontar Feb 26 '09 at 20:17
1

upvoted as was comparing `return date.AddDays(-(date.Day-1))` versus `return new DateTime(date.Year, date.Month, 1);` and the performance of the first over 2000 iterations is better (923ms newing up versus 809ms returning the same object) – Terry_Brown Apr 02 '12 at 10:28

score 13 · Answer 3 · edited Feb 22 '16 at 09:20

13

using Fluent DateTime https://github.com/FluentDateTime/FluentDateTime

        var lastMonth = 1.Months().Ago().Date;
        var firstDayOfMonth = lastMonth.FirstDayOfMonth();
        var lastDayOfMonth = lastMonth.LastDayOfMonth();

edited Feb 22 '16 at 09:20

shriek

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answered Sep 04 '09 at 12:13

Simon

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Franci Penov · Answer 4 · 2009-02-26T18:37:21.380

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DateTime LastMonthLastDate = DateTime.Today.AddDays(0 - DateTime.Today.Day);
DateTime LastMonthFirstDate = LastMonthLastDate.AddDays(1 - LastMonthLastDate.Day);

edited Feb 26 '09 at 18:37

answered Feb 26 '09 at 18:25

Franci Penov

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DateTime.Today.Days -> 'System.DateTime' does not contain a definition for 'Days'... – andleer Feb 26 '09 at 18:29

score 6 · Answer 5 · answered May 06 '14 at 13:44

6

I use this simple one-liner:

public static DateTime GetLastDayOfPreviousMonth(this DateTime date)
{
    return date.AddDays(-date.Day);
}

Be aware, that it retains the time.

answered May 06 '14 at 13:44

1

Just what I wanted, concise expression I could use inside a ternary. Thanks! – Joe Ballard Sep 19 '16 at 21:00
Works great, but how does it work? would be good to know.. – Musaffar Patel Dec 22 '22 at 18:53

score 4 · Answer 6 · edited Oct 21 '12 at 00:25

4

The canonical use case in e-commerce is credit card expiration dates, MM/yy. Subtract one second instead of one day. Otherwise the card will appear expired for the entire last day of the expiration month.

DateTime expiration = DateTime.Parse("07/2013");
DateTime endOfTheMonthExpiration = new DateTime(
  expiration.Year, expiration.Month, 1).AddMonths(1).AddSeconds(-1);

edited Oct 21 '12 at 00:25

Konrad Viltersten

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answered Jun 10 '12 at 16:17

MartinLeo

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score 4 · Answer 7 · edited Nov 30 '12 at 08:46

An approach using extension methods:

class Program
{
    static void Main(string[] args)
    {
        DateTime t = DateTime.Now;

        DateTime p = t.PreviousMonthFirstDay();
        Console.WriteLine( p.ToShortDateString() );

        p = t.PreviousMonthLastDay();
        Console.WriteLine( p.ToShortDateString() );


        Console.ReadKey();
    }
}


public static class Helpers
{
    public static DateTime PreviousMonthFirstDay( this DateTime currentDate )
    {
        DateTime d = currentDate.PreviousMonthLastDay();

        return new DateTime( d.Year, d.Month, 1 );
    }

    public static DateTime PreviousMonthLastDay( this DateTime currentDate )
    {
        return new DateTime( currentDate.Year, currentDate.Month, 1 ).AddDays( -1 );
    }
}

See this link http://www.codeplex.com/fluentdatetime for some inspired DateTime extensions.

score 1 · Answer 8 · answered Apr 15 '16 at 18:08

This is a take on Mike W's answer:

internal static DateTime GetPreviousMonth(bool returnLastDayOfMonth)
{
    DateTime firstDayOfThisMonth = DateTime.Today.AddDays( - ( DateTime.Today.Day - 1 ) );
    DateTime lastDayOfLastMonth = firstDayOfThisMonth.AddDays (-1);
    if (returnLastDayOfMonth) return lastDayOfLastMonth;
    return firstDayOfThisMonth.AddMonths(-1);
}

You can call it like so:

dateTimePickerFrom.Value = GetPreviousMonth(false);
dateTimePickerTo.Value = GetPreviousMonth(true);

Maksym Gontar · Answer 9 · 2009-02-26T19:13:01.500

1

DateTime now = DateTime.Now;
int prevMonth = now.AddMonths(-1).Month;
int year = now.AddMonths(-1).Year;
int daysInPrevMonth = DateTime.DaysInMonth(year, prevMonth);
DateTime firstDayPrevMonth = new DateTime(year, prevMonth, 1);
DateTime lastDayPrevMonth = new DateTime(year, prevMonth, daysInPrevMonth);
Console.WriteLine("{0} {1}", firstDayPrevMonth.ToShortDateString(),
  lastDayPrevMonth.ToShortDateString());

edited Feb 26 '09 at 19:13

answered Feb 26 '09 at 18:29

Maksym Gontar

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What if DateTime.Now yields 2009-01-31 on the first call and 2009-02-01 on the second call? – Amy B Feb 26 '09 at 18:42

score 1 · Answer 10 · answered Feb 26 '09 at 18:35

If there's any chance that your datetimes aren't strict calendar dates, you should consider using enddate exclusion comparisons... This will prevent you from missing any requests created during the date of Jan 31.

DateTime now = DateTime.Now;
DateTime thisMonth = new DateTime(now.Year, now.Month, 1);
DateTime lastMonth = thisMonth.AddMonths(-1);

var RequestIds = rdc.request
  .Where(r => lastMonth <= r.dteCreated)
  .Where(r => r.dteCreated < thisMonth)
  .Select(r => r.intRequestId);

score 1 · Answer 11 · answered Dec 21 '22 at 10:34

1

var lastMonth = DateTime.Today.AddMonths(-1);
dRet1 = new DateTime(lastMonth.Year, lastMonth.Month, 1);
dRet2 = new DateTime(lastMonth.Year, lastMonth.Month, DateTime.DaysInMonth(lastMonth.Year, lastMonth.Month));

answered Dec 21 '22 at 10:34

Ahmed Elzeiny

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Get the previous month's first and last day dates in c#

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