Help with WEEKNUM Formula

[watson150]

I have the date 31/12/2019 in cell B3 - In the next cell I have =WEEKNUM(B3,2)

But this returns 53

In our production, Week 1 runs from 30/12/2019 to 05/1/2020 - Is there any way this can be adjusted to suit?

[Ron Coderre]

Here's something to try:

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Is that something you can work with?

[FlameRetired]

I also tried =WEEKNUM(B3,21)

	B	C
3	12/30/2019	1
4	12/31/2019	1
5	1/1/2020	1
6	1/2/2020	1
7	1/3/2020	1
8	1/4/2020	1
9	1/5/2020	1
10	1/6/2020	2
11	1/7/2020	2
12	1/8/2020	2
13	1/9/2020	2
14	1/10/2020	2
15	1/11/2020	2
16	1/12/2020	2
17	1/13/2020	3
18	1/14/2020	3
19	1/15/2020	3
20	1/16/2020	3
21	1/17/2020	3
22	1/18/2020	3
23	1/19/2020	3
24	1/20/2020	4

[hrlngrv]

Do you mean the M-Su week in which 1 Jan falls is always week 1?

FWIW, ISO week numbers are a bit different. Non-leap years which begin on Thursdays or leap years which begin on Wednesday or Thursday have 53 Thusdays, so have 53 weeks. You may want ISO week numbers. If so, try =ISOWEEKNUM(B3).

[FlameRetired]

@ hrlngrv

Isn't that what my formula does? =WEEKNUM(B3,21)

Or am I missing something?

[hrlngrv]

Isn't that what my formula does? =WEEKNUM(B3,21) . . .

Yes, but ISOWEEKNUM is more explicit. Magic numbers like the 21 as 2nd argument are best avoided whenever possible, IMO.