Date subtration

[graham]

Hi,

I need to subtract one date from another, giving the result in months. However, the following code does not seem to give the correct answer:

// ----------------- subtract dates and find difference in months --------------------
list ($year1, $month1, $day1) = explode ("-", $min_date);
list ($year2, $month2, $day2) = explode ("-", $max_date);
$timestamp1 = mktime(0,0,0, $month1, $day1, $year1);
$timestamp2 = mktime(0,0,0, $month2, $day2, $year2);
$diff = ($timestamp1 > $timestamp2) ? ($timestamp1 - $timestamp2) : ($timestamp2 - $timestamp1);
$years_diff = date("Y", $diff) - 1970;
if ($years_diff > 0){
$yearstomonths = $years_diff / 12;
}else{
$yearstomonths = 0;
}
$numberofmonths = $yearstomonths + date("m", $diff)-1;

Could someone please advise me where I'm going wrong?

cheers, Graham

[Anon]

Ok. I'm not sure where you are going wrong, but here is a simple function I cooked up for a period diff. Give it two variables, in the form MMYYYY and it will give you the difference in months between them.

function period_diff($first, $second) {
$fmonth=substr($first,0,2);$fyear=substr($first,-4);
$smonth=substr($second,0,2);$syear=substr($second,-4);

return abs((((($syear - $fyear) 12) - $fmonth) + $smonth));
}

Hope that helps 🙂

Chris King

[Anon]

Hrmm .. that should be ($syear - $fyear) * 12

.. damn should read over these things 🙂

Chris King

[[deleted]]

why don't you just take the $diff, which is the number of seconds between the two dates, and revide it by the number of seconds in a month?

[[deleted]]

Okie, that would not be precise. back to the drawing board :-)

[[deleted]]

why on earth are you deviding the number of years by 12? :-)

try this:

$min_date="1972-10-01";
$max_date="1972-11-01";

list ($year1, $month1, $day1) = explode ("-", $min_date);
list ($year2, $month2, $day2) = explode ("-", $max_date);
$timestamp1 = mktime(0,0,0, $month1, $day1, $year1);
$timestamp2 = mktime(0,0,0, $month2, $day2, $year2);
$diff=abs($timestamp2 - $timestamp1);
list($months,$years)=explode(' ', date("m Y",$diff));
echo $months+(12*($years - 1970))-1;