PHP Week number [duplicate]

Question

This question already has answers here:

How to get year-sensitive calendar week ? date("W") gives back 52 for 1st of January (4 answers)

Getting year and week of year from PHP date() when week spans two years (1 answer)

Closed 8 years ago.

date_default_timezone_set('Europe/Helsinki');
$now = strtotime('now'); // 1388430373
$weekNumber = date('W', $now);
var_dump($weekNumber);

Why this code shows 01?
It's now 30th december 2013

How to get right week number?

Answer 1

This week is the first week of the new year. That is the right week number.

PS: Last week was #52: echo date('W', strtotime('-1 week')); Output: 52. A year only has 52 weeks so...

Answer 2

ISO 8601 week number is based on WEEK 01 which is

• the week with the year's first Thursday in it (the formal ISO definition)

which is

• the week with 4 January in it,
• the first week with the majority (four or more) of its days in the starting year,
• the week starting with the Monday in the period 29 December – 4 January.

where a week is defined as beginning with Monday and ending with Sunday

EDIT

Depending on your definition of week number, you might consider

$weekNumber = floor(date('z', $now) / 7) + 1;

which will give the number of 7-day periods since 1st January, but it will vary from year to year which day of the week is the week start day