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

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

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

if the day itself doesn't matter do this:

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

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.