Subtracts a year from a given timestamp

 
<?
    print strtotime("1 year ago", 123456789);
?>

1.	Calculating a date interval with strtotime()
2.	Checking a date range
3.	int strtotime ( string time [, int now] ) converts strings to a timestamp
4.	Using strtotime()
5.	Using strtotime() with a starting epoch timestamp
6.	Find the First monday on or after November 1, 2008
7.	Find weekday
8.	Finding the Date for a Weekday
9.	Getting the Day and Week of the Year
10.	If PHP is unable to convert your string into a timestamp, it will return -1.
11.	Obtaining the Difference Between Two Dates

Subtracts a year from a given timestamp : strtotime « String « PHP