Get date of first Monday of the week?

Question

I was wondering if you guys know how to get the date of currents week's monday based on todays date?

i.e 2009-11-03 passed in and 2009-11-02 gets returned back

/M

Have a look at this question: http://stackoverflow.com/questions/38039/how-can-i-get-the-datetime-for-the-start-of-the-week — Tom van Enckevort, Nov 03 '09 at 07:53

score 130 · Accepted Answer · answered Nov 03 '09 at 07:54

130

This is what i use (probably not internationalised):

DateTime input = //...
int delta = DayOfWeek.Monday - input.DayOfWeek;
DateTime monday = input.AddDays(delta);

answered Nov 03 '09 at 07:54

Pondidum

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Yes, indeed: Not internationalized. Monday is not always the first day of week. – Serge Wautier Nov 03 '09 at 07:58
16

You can get the first day of week using: CultureInfo.CurrentCulture.DateTimeFormat.FirstDayOfWeek – Shay Erlichmen Nov 03 '09 at 08:03
13

Actually the first day of the week according to culture is of no interest in this case; the OP wants the monday of the week, not the first day of the week. – Fredrik Mörk Nov 03 '09 at 08:28
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-1. Given a Sunday, this returns the next day, rather than 6 days ago. (`DayOfWeek.Monday` is `1`, `input.DayOfWeek` is `0` for a Sunday.) – Rawling Jan 22 '13 at 09:57
@Rawling: Hence the "not internationalised" in my answer - in the UK, Sunday is the first day of the week, so the following day is the Monday of that week. – Pondidum Jan 22 '13 at 11:24
2

Apologies and don't take it personally, I just wanted to voice a dissenting opinion for people who Google "first day of week" and get this. (Interesting that you give Sunday as fdow for UK, as in the `en-GB` culture it's Monday.) – Rawling Jan 22 '13 at 12:26
1

@Rawling: It's defiantly something to be aware of - why can't it be the same everywhere? :( – Pondidum Jan 22 '13 at 13:28
If the 'input' is 1/1/2017 (a Sunday) this code gives 2/1/2017 (the following Monday and the beginning of a new week!) as the first day of the week?!?!?!? – Paul Zahra Aug 26 '16 at 08:52
var weekStart = input.AddDays(now.DayOfWeek == DayOfWeek.Sunday ? -6 : DayOfWeek.Monday - input.DayOfWeek); – Paito Jan 08 '20 at 14:21

score 64 · Answer 2 · answered Dec 02 '11 at 11:29

64

The Pondium answer can search Forward in some case. If you want only Backward search I think it should be:

DateTime input = //...
int delta = DayOfWeek.Monday - input.DayOfWeek;
if(delta > 0)
    delta -= 7;
DateTime monday = input.AddDays(delta);

answered Dec 02 '11 at 11:29

Marco

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This should be the proper answer as it handles Sundays, i.e. FirstDayOfWeek is Monday, so if Sunday is the input date it should return the Monday before. The accepted answer does not. – J_D Apr 24 '14 at 13:51
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+1 If the 'input' is 1/1/2017 (a Sunday) this code gives 26/12/2016 as the first day of the week! Not 2/1/2017 (which the accepted answer gives!) – Paul Zahra Aug 26 '16 at 08:59
1

It also works for 01/01/2019 = 31/12/2018! – Paul Zahra Aug 26 '16 at 09:12
var monday = DateTime.Now.AddDays(DayOfWeek.Monday - DateTime.Now.DayOfWeek > 0 ? (DayOfWeek.Monday - DateTime.Now.DayOfWeek) - 7 : DayOfWeek.Monday - DateTime.Now.DayOfWeek).Date; – aBetterGamer Oct 03 '17 at 18:47
This is worked for me. Also on sunday or monday. It's just work! Thanks – Agus Sapurta Sijabat Sep 21 '20 at 02:26
Yes, this handles sundays properly! – Akos Lukacs Oct 21 '20 at 20:06

score 8 · Answer 3 · answered Nov 03 '09 at 07:54

8

Something like this would work

DateTime dt = DateTime.Now;
while(dt.DayOfWeek != DayOfWeek.Monday) dt = dt.AddDays(-1);

I'm sure there is a nicer way tho :)

answered Nov 03 '09 at 07:54

PaulB

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score 6 · Answer 4 · answered Sep 03 '14 at 08:04

public static class DateTimeExtension
{
    public static DateTime GetFirstDayOfWeek(this DateTime date)
    {
        var firstDayOfWeek = CultureInfo.CurrentCulture.DateTimeFormat.FirstDayOfWeek;

        while (date.DayOfWeek != firstDayOfWeek)
        {
            date = date.AddDays(-1);
        }

        return date;
    }
}

International here. I think as extension it can be more useful.

score 3 · Answer 5 · answered May 17 '14 at 18:24

3

What about:

CultureInfo.CurrentCulture.DateTimeFormat.FirstDayOfWeek

Why don't use native solution?

answered May 17 '14 at 18:24

Gh61

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The question is to get the specific date (i.e. 2015-11-20) not which day is defined as the first day. – Michael Blackburn Nov 20 '15 at 18:11

HelloWorld · Answer 6 · 2013-09-16T08:03:51.570

1

var now = System.DateTime.Now;

var result = now.AddDays(-((now.DayOfWeek - System.Threading.Thread.CurrentThread.CurrentCulture.DateTimeFormat.FirstDayOfWeek + 7) % 7)).Date;

Probably will return you with Monday. Unless you are using a culture where Monday is not the first day of the week.

edited Sep 16 '13 at 08:03

answered Sep 13 '13 at 14:08

HelloWorld

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score 0 · Answer 7 · answered Nov 03 '09 at 07:55

0

Try this:

public DateTime FirstDayOfWeek(DateTime date)
{
    var candidateDate=date;
    while(candidateDate.DayOfWeek!=DayOfWeek.Monday) {
        candidateDate=candidateDate.AddDays(-1);
    }
    return candidateDate;
}

EDIT for completeness: overload for today's date:

public DateTime FirstDayOfCurrentWeek()
{
    return FirstDayOfWeek(DateTime.Today);
}

answered Nov 03 '09 at 07:55

Konamiman

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Why looping??, there are ways to-do it without a loop. See answers below. – Shay Erlichmen Nov 03 '09 at 07:59

Get date of first Monday of the week?

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