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

Flashbulb

all u want is month and year? no day? – Normandnormandy

Could you clarify exactly what inputs/outputs and expected behavior you're wanting? – Roxi

@Mai thank you for your comment! Please rather than suggesting solutions via comments, create an answer instead. That way there can be a conversation around your answer, as well as gathering votes. – Flashbulb

@Flashbulb agreed and have posted as answer – Mai

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

Aruabea

Also, my tz::date() function internally uses DateTime object to do timezone or time adjustments. – Flashbulb

@mr.b: Glad I could help. Are you using the DateTimeZone class in your tz::date() function? ca2.php.net/manual/en/class.datetimezone.php – Aruabea

tz class is a convenience wrapper around TzDate class. See pastebin.com/GzUcvvA0, perhaps you might find it useful. Code should be self-explanatory. tz class is here pastebin.com/8mcRu5qe; however, it's not standalone, as I use Kohana framework, and it is tied with some other classes it offers. – Flashbulb

Answer 2

if the day itself doesn't matter do this:

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

Dupondius

Today, that still comes out as March. I'd expect it to be February. – Attlee

@codecraft then try it like this: echo date('Y-m-d', strtotime(date('Y-m-d')." -1 month")); – Dupondius

For me, both those lines give me 2011-03-02. Weird. – Attlee

damn >< had a litle error in it: echo date('Y-m-d', strtotime(date('Y-m-1')." -1 month")); this is what i ment – Dupondius

Codecraft: Twelve years later, SeanDowney's answer on why it's mistaken as a bug is worth a read. Be wary when doing these operations in general if the present day is 28-31 of the month. – Willpower

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.

Snick

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

Logjam

This is a better solution to me. Though I would suggest cloning $d before modifying it as this will change the value of $d completely since its a TimeDate object. $d2 = clone $d and then call modify() on $d2 like $d2->modify('first day of previous month') so that $d and $d2 stay different. – Natalienatalina

@AllanDereal in that case DateTimeImmutable is more appropriate – Logjam

Answer 5

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

Perce

This is perfect. By using first day it prevents things like Feb 31, June 31, etc. – Dearly

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()))

Turret

Really nice and short code, is there any same option for mysql? ie: CURDATE()-$day //30 but it's not return true month if current month is 31 days. – Lahdidah

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

Normandnormandy

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'))));

Kongo

Programming aside, if I stopped you in the street today (30th March 2011) and asked you what the date was this time last month - and that you HAD to give an answer, would you honestly reply "3rd March"? I wouldn't! – Attlee

@Codecraft: perhaps the right answer would be "there was no such time", as there really was no "this time, one month ago". But there really WAS this time one month ago, it just depends on definition of "one month ago". I guess this whole problem is caused by that definition. – Flashbulb

@dqhendricks: I didn't mention specific dates, did I? :) Also, interesting choice of days to subtract - how did strtotime come to a conclusion that I wanted to substract as many days as February had? Why not as many days as current month has? Just weird. – Flashbulb

@Flashbulb perhaps since we asked for last month, it figured out how many days were in last month, and subtracted them haha. if it subtracted this months numbers of days, there would be other types of errors. subtracting a month from march first would return a january date. – Kongo

Answer 9

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

would solve this

Mai

Your solution had worked well for me a long time back but now it came back to bite me. It has the same issue which some call it bug (it's not). It won't give you February when called on say 29-31 March because ignoring leap year, 29-31 Feb doesn't exist. In my case, I did date("m-Y", strtotime("-6 months")) (with my current date 31 Aug 2023) which returns "03-2023"--when we want Feb 2023. Using date("m-Y", strtotime("last day of -6 month")) helped me fix it. Adding this or a clarification in your answer would be good. – Willpower

Answer 10

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;

Kynan

How is it not a bug? A month is an ill-defined unit without context, and the function lacks contextual support for it. – Kynan

It's not a bug as discussed in the comments and explained in SeanDowney's answer above. But yes, most of us agree that adding some mention of this behaviour in the function would save many of us the trouble. A month is an ill-defined unit in the end and I'll quote this infamous comment by rasmus from a closed 2003 bug report on php.net, "If I told you on January 30 that I would come back in exactly one month to beat the crap out of you, when would you think I would show up?" – Willpower

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'));
}

Sholley

Answer 12

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 ;-)

Attlee

Actually, thats really interesting. I would expect and want this code to result in 28th Feb or 1st March, but definately not 3rd March! I call bug! – Attlee

Well, it all really depends on what do you expect, I think. That's why I've been careful enough not to call it a bug off the bat, because it might be desired functionality. If I asked for date('Y-m-d', strtotime('last month')), on 31st of march, which date should it return? Last day of February? I'm not quite sure.. Perhaps someone with more experience in the area can shed some light on why is this how strtotime behaves.. – Flashbulb

You're quite right, for me, its strange behavior but I guess this is one of those questions that may not have a 'right' answer. – Attlee

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);
}

Chiekochien

While this code snippet may solve the problem, it doesn't explain why or how it answers the question. Please include an explanation for your code, as that really helps to improve the quality of your post. Remember that you are answering the question for readers in the future, and those people might not know the reasons for your code suggestion. Flaggers / reviewers: For code-only answers such as this one, downvote, don't delete! – Samal

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

Amador

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.

Interview

Answer 16

Not short, but it works. (It's shorter if you remove my comments)

// Calculate number of days in the current month      
$currentday = date('d');

// Calculate number of days in the previous month
$dayslastmonth = date("t", mktime(0,0,0, date("n") - 1));

// Get the year and month for last month    
$lastmonthyear = date('Y-m', strtotime(date('Y-m')." -1 month"));
    
// If the current day is greater than the last day of last month
// set the day for last month equal to the current day
if($currentday <= $dayslastmonth){
  $daylastmonth = $currentday;
else{
  $daylastmonth = $dayslastmonth;
}
   
// Put it all together
$datelastmonth = $lastmonthyear."-".$daylastmonth;

Plossl