How to get previous month and year relative to today, using strtotime and date?

Question

I need to get previous month and year, relative to current date.

However, see following example.

// Today is 2011-03-30
echo date('Y-m-d', strtotime('last month'));

// Output:
2011-03-02

This behavior is understandable (to a certain point), due to different number of days in february and march, and code in example above is what I need, but works only 100% correctly for between 1st and 28th of each month.

So, how to get last month AND year (think of date("Y-m")) in the most elegant manner as possible, which works for every day of the year? Optimal solution will be based on strtotime argument parsing.

Update. To clarify requirements a bit.

I have a piece of code that gets some statistics of last couple of months, but I first show stats from last month, and then load other months when needed. That's intended purpose. So, during THIS month, I want to find out which month-year should I pull in order to load PREVIOUS month stats.

I also have a code that is timezone-aware (not really important right now), and that accepts strtotime-compatible string as input (to initialize internal date), and then allows date/time to be adjusted, also using strtotime-compatible strings.

I know it can be done with few conditionals and basic math, but that's really messy, compared to this, for example (if it worked correctly, of course):

echo tz::date('last month')->format('Y-d')

So, I ONLY need previous month and year, in a strtotime-compatible fashion.

Answer (thanks, @dnagirl):

// Today is 2011-03-30
echo date('Y-m-d', strtotime('first day of last month')); // Output: 2011-02-01

Answer 1

Have a look at the DateTime class. It should do the calculations correctly and the date formats are compatible with strttotime. Something like:

$datestring='2011-03-30 first day of last month';
$dt=date_create($datestring);
echo $dt->format('Y-m'); //2011-02

Answer 2

if the day itself doesn't matter do this:

echo date('Y-m-d', strtotime(date('Y-m')." -1 month"));

Answer 3

I found an answer as I had the same issue today which is a 31st. It's not a bug in php as some would suggest, but is the expected functionality (in some since). According to this post what strtotime actually does is set the month back by one and does not modify the number of days. So in the event of today, May 31st, it's looking for April-31st which is an invalid date. So it then takes April 30 an then adds 1 day past it and yields May 1st.

In your example 2011-03-30, it would go back one month to February 30th, which is invalid since February only has 28 days. It then takes difference of those days (30-28 = 2) and then moves two days past February 28th which is March 2nd.

As others have pointed out, the best way to get "last month" is to add in either "first day of" or "last day of" using either strtotime or the DateTime object:

// Today being 2012-05-31
//All the following return 2012-04-30
echo date('Y-m-d', strtotime("last day of -1 month"));
echo date('Y-m-d', strtotime("last day of last month"));
echo date_create("last day of -1 month")->format('Y-m-d'); 

// All the following return 2012-04-01
echo date('Y-m-d', strtotime("first day of -1 month")); 
echo date('Y-m-d', strtotime("first day of last month"));
echo date_create("first day of -1 month")->format('Y-m-d');

So using these it's possible to create a date range if your making a query etc.

Answer 4

If you want the previous year and month relative to a specific date and have DateTime available then you can do this:

$d = new \DateTimeImmutable('2013-01-01', new \DateTimeZone('UTC')); 
$firstDay = $d->modify('first day of previous month');
$year = $firstDay->format('Y'); //2012
$month = $firstDay->format('m'); //12

Answer 5

date('Y-m', strtotime('first day of last month'));

Answer 6

strtotime have second timestamp parameter that make the first parameter relative to second parameter. So you can do this:

date('Y-m', strtotime('-1 month', time()))

Answer 7

if i understand the question correctly you just want last month and the year it is in:

<?php

  $month = date('m');
  $year = date('Y');
  $last_month = $month-1%12;
  echo ($last_month==0?($year-1):$year)."-".($last_month==0?'12':$last_month);

?>

Here is the example: http://codepad.org/c99nVKG8

Answer 8

ehh, its not a bug as one person mentioned. that is the expected behavior as the number of days in a month is often different. The easiest way to get the previous month using strtotime would probably be to use -1 month from the first of this month.

$date_string = date('Y-m', strtotime('-1 month', strtotime(date('Y-m-01'))));

Answer 9

I think you've found a bug in the strtotime function. Whenever I have to work around this, I always find myself doing math on the month/year values. Try something like this:

$LastMonth = (date('n') - 1) % 12;
$Year      =  date('Y') - !$LastMonth;

Answer 10

Perhaps slightly more long winded than you want, but i've used more code than maybe nescessary in order for it to be more readable.

That said, it comes out with the same result as you are getting - what is it you want/expect it to come out with?

//Today is whenever I want it to be.
$today = mktime(0,0,0,3,31,2011);

$hour   = date("H",$today);
$minute = date("i",$today);
$second = date("s",$today);
$month  = date("m",$today);
$day    = date("d",$today);
$year   = date("Y",$today);

echo "Today: ".date('Y-m-d', $today)."<br/>";
echo "Recalulated: ".date("Y-m-d",mktime($hour,$minute,$second,$month-1,$day,$year));

If you just want the month and year, then just set the day to be '01' rather than taking 'todays' day:

 $day = 1;

That should give you what you need. You can just set the hour, minute and second to zero as well as you aren't interested in using those.

 date("Y-m",mktime(0,0,0,$month-1,1,$year);

Cuts it down quite a bit ;-)

Answer 11

This is because the previous month has less days than the current month. I've fixed this by first checking if the previous month has less days that the current and changing the calculation based on it.

If it has less days get the last day of -1 month else get the current day -1 month:

if (date('d') > date('d', strtotime('last day of -1 month')))
{
    $first_end = date('Y-m-d', strtotime('last day of -1 month'));
}
else
{
    $first_end = date('Y-m-d', strtotime('-1 month'));
}

Answer 12

date("m-Y", strtotime("-1 months")); 

would solve this

Answer 13

If a DateTime solution is acceptable this snippet returns the year of last month and month of last month avoiding the possible trap when you run this in January.

function fn_LastMonthYearNumber()
{
 $now = new DateTime();
 $lastMonth = $now->sub(new DateInterval('P1M'));
 $lm= $lastMonth->format('m');
 $ly= $lastMonth->format('Y');
 return array($lm,$ly);
}

Answer 14

//return timestamp, use to format month, year as per requirement
function getMonthYear($beforeMonth = '') {
    if($beforeMonth !="" && $beforeMonth >= 1) {
        $date = date('Y')."-".date('m')."-15";
        $timestamp_before = strtotime( $date . ' -'.$beforeMonth.' month' );
        return $timestamp_before;
    } else {
        $time= time();
        return $time;
    }
}


//call function
$month_year = date("Y-m",getMonthYear(1));// last month before  current month
$month_year = date("Y-m",getMonthYear(2)); // second last month before current month

Answer 15

function getOnemonthBefore($date){
    $day = intval(date("t", strtotime("$date")));//get the last day of the month
    $month_date = date("y-m-d",strtotime("$date -$day days"));//get the day 1 month before
    return $month_date;
}

The resulting date is dependent to the number of days the input month is consist of. If input month is february (28 days), 28 days before february 5 is january 8. If input is may 17, 31 days before is april 16. Likewise, if input is may 31, resulting date will be april 30.

NOTE: the input takes complete date ('y-m-d') and outputs ('y-m-d') you can modify this code to suit your needs.