Get the Number of Weeks Between Two Dates

Get the number of weeks between two Dates.

It is pretty easy with joda time:

DateTime dateTime1 = new DateTime(date1);
DateTime dateTime2 = new DateTime(date2);

int weeks = Weeks.weeksBetween(dateTime1, dateTime2).getWeeks();

Count number of including weeks between 2 dates

The simplest way is probably to write a method to get the start of a week. Then you can subtract one date from another, divide the number of days by 7 and add 1 (to make it inclusive).

Personally I'd use Noda Time for all of this, but using DateTime:

// Always uses Monday-to-Sunday weeks
public static DateTime GetStartOfWeek(DateTime input)
{
    // Using +6 here leaves Monday as 0, Tuesday as 1 etc.
    int dayOfWeek = (((int) input.DayOfWeek) + 6) % 7;
    return input.Date.AddDays(-dayOfWeek);
}

public static int GetWeeks(DateTime start, DateTime end)
{
    start = GetStartOfWeek(start);
    end = GetStartOfWeek(end);
    int days = (int) (end - start).TotalDays;
    return (days / 7) + 1; // Adding 1 to be inclusive
}

Complete example:

using System;

class Program
{
    static void Main (string[] args)
    {
        ShowWeeks(new DateTime(2016, 9, 17), new DateTime(2016, 9, 26));
        ShowWeeks(new DateTime(2016, 9, 17), new DateTime(2016, 9, 25));
        ShowWeeks(new DateTime(2016, 9, 19), new DateTime(2016, 9, 26));
        ShowWeeks(new DateTime(2016, 9, 12), new DateTime(2016, 9, 25));
    }

    static void ShowWeeks(DateTime start, DateTime end)
    {
        int weeks = GetWeeks(start, end);
        Console.WriteLine($"{start:d} {end:d} {weeks}");
    }

    // Always uses Monday-to-Sunday weeks
    public static DateTime GetStartOfWeek(DateTime input)
    {
        // Using +6 here leaves Monday as 0, Tuesday as 1 etc.
        int dayOfWeek = (((int) input.DayOfWeek) + 6) % 7;
        return input.Date.AddDays(-dayOfWeek);
    }

    public static int GetWeeks(DateTime start, DateTime end)
    {
        start = GetStartOfWeek(start);
        end = GetStartOfWeek(end);
        int days = (int) (end - start).TotalDays;
        return (days / 7) + 1; // Adding 1 to be inclusive
    }
}

Output (in my UK locale):

17/09/2016 26/09/2016 3
17/09/2016 25/09/2016 2
19/09/2016 26/09/2016 2
12/09/2016 25/09/2016 2

PHP - calculating the number of weeks between two dates

The dates you pass to strtotime need to be enclosed in quotes. And the correct answer is indeed 3, as there are 3 weeks, 6 days, 23 hours and 59 minutes between the two times. Try this:

$HowManyWeeks = date( 'W', strtotime( '2019-04-21 23:59:00' ) ) - date( 'W', strtotime( '2019-03-25 00:00:00' ) );
echo $HowManyWeeks;

As has been pointed out, this will only work when the weeks are in the same year. It's easier to use DateTime objects as in @MiroslavGlamuzina answer or you can simply divide the strtotime difference by 604800 (seconds in a week); you can then take the floor or ceil if required to convert to an integer value:

$HowManyWeeks = (strtotime( '2019-04-21 23:59:00' ) - strtotime( '2019-03-25 00:00:00' )) / 604800;
echo $HowManyWeeks;

Output:

3.9939484126984

Demo on 3v4l.org

Most efficient way to count number of weeks between two datetimes

Get the number of days and divide by 7.

int weeks = (date1 - date2).TotalDays / 7;

You may well have a remainder of up to 6 days that will not be included in the number of weeks.

How create field weeks in between two dates

Method 1: Using list comprehension, dt.period & getattr

provided by Jon Clements in comments

This method will work when years change between the compared dates:

cw['weeks_diff'] = (
    [getattr(el, 'n', 0) 
     for el in cw['lead_date'].dt.to_period('W') - cw['Received_date'].dt.to_period('W')]
)

---

Method 2: using weeknumbers with dt.strftime('%W')

We can use pd.to_datetime to convert your dates to datetime. Then we use the dt.strftime accessor to get the weeknumbers with %W.

Finally we substract both weeknumbers:

weeks = (cw[['lead_date', 'Received_date']]
         .apply(lambda x: pd.to_datetime(x).dt.strftime('%W'))
         .replace('NaT', 0)
         .astype(int)
        )

cw['weeks_diff'] = weeks['lead_date'] - weeks['Received_date']

    lead_date Received_date  weeks_diff
0  2019-12-28    2019-12-15           2
1  2019-12-23    2019-12-21           1

How to calculate the amount of weeks between two week pickers

there are 52 weeks + 1 day in a year and 52 weeks + 2 days in a leap year. So your suggestion amountOfWeeks += yearDiff * 52; does not seem accurate. The below function converts the start and end year and weeks into miliseconds, subract and convert back into weeks. It should work with leap years. I haven't tested it though.

function compareWeeks(startYear, startWeek, endYear, endWeek) {
    
    const start =
        new Date(startYear, 0).getTime() + startWeek * 7 * 24 * 60 * 60 * 1000

    const end = 
        new Date(endYear, 0).getTime() + endWeek * 7 * 24 * 60 * 60 * 1000

    const diff = Math.abs(end - start)
    const diffWeeks = diff / 1000 / 60 / 60 / 24 / 7
    return diffWeeks
}

Update for ISO-week-numbering year (your use case):

According to the wikipedia, an ISO Year has either 52 or 53(ISO Leap Year) weeks. 53 when it starts or ends with Thirsday else 52. Checkout the below code:

function weeksInBetween(startYear, startWeek, endYear, endWeek) {
    let diff = 0
    for (let i = startYear; i < endYear; i++) {
        const has53Weeks = isISOLeapYear(i)
        if (has53Weeks) {
            diff += 53
        } else {
            diff += 52
        }
    }

    return (diff += endWeek - --startWeek)
    /* 
        the '--startWeek' makes sure the starting week
        is not subtracted from the result, because you
        want the result to be inclusive'
        
    */
}

function isISOLeapYear(year) {
    const startsWithThursday =
        new Date(year, 0, 1).toString().split(' ')[0] === 'Thu'
    const endsWithThursday =
        new Date(year, 11, 31).toString().split(' ')[0] === 'Thu'

    if (startsWithThursday || endsWithThursday) {
        return true
    }

    return false
}

console.log(
    weeksInBetween(2020, 1, 2021, 52), // 105
    weeksInBetween(2009, 1, 2010, 52), // 105
    weeksInBetween(2021, 1, 2021, 52), // 52
    weeksInBetween(2021, 1, 2022, 52), // 104
    weeksInBetween(2021, 1, 2021, 1)   // 1
)

---

Related Topics