(PHP 5.5.0, PECL >= 3.0.0a1)
IntlCalendar::fieldDifference — Calculate difference between given time and this objectʼs time
Object oriented style
$when
   , int $field
   )Procedural style
   Return the difference between the given time and the time this object is
   set to, with respect to the quantity specified the
   field parameter.
  
This method is meant to be called successively, first with the most significant field of interest down to the least significant field. To this end, as a side effect, this calendarʼs value for the field specified is advanced by the amount returned.
calThe IntlCalendar resource.
when
      The time against which to compare the quantity represented by the
      field. For the result to be positive, the time
      given for this parameter must be ahead of the time of the object the
      method is being invoked on.
     
fieldThe field that represents the quantity being compared.
 One of the IntlCalendar date/time field constants. These are integer
 values between 0 and
 IntlCalendar::FIELD_COUNT.
   Returns a (signed) difference of time in the unit associated with the
   specified field or FALSE on failure.
  
Example #1 IntlCalendar::fieldDifference()
<?php
ini_set('date.timezone', 'Europe/Lisbon');
ini_set('intl.default_locale', 'fr_FR');
$cal1 = IntlCalendar::fromDateTime('2012-02-29 09:00:11');
$cal2 = IntlCalendar::fromDateTime('2013-03-01 09:19:29');
$time = $cal2->getTime();
echo "Time before: ", IntlDateFormatter::formatObject($cal1), "\n";
printf(
    "The difference in time is %d year(s), %d month(s), "
  . "%d day(s), %d hour(s) and %d minute(s)\n",
    $cal1->fieldDifference($time, IntlCalendar::FIELD_YEAR),
    $cal1->fieldDifference($time, IntlCalendar::FIELD_MONTH),
    $cal1->fieldDifference($time, IntlCalendar::FIELD_DAY_OF_MONTH),
    $cal1->fieldDifference($time, IntlCalendar::FIELD_HOUR_OF_DAY),
    $cal1->fieldDifference($time, IntlCalendar::FIELD_MINUTE)
);
//now it was advanced to the target time, exception for the seconds,
//for which we did not measure the difference
echo "Time after: ", IntlDateFormatter::formatObject($cal1), "\n";
The above example will output:
Time before: 29 févr. 2012 09:00:11 The difference in time is 1 year(s), 0 month(s), 1 day(s), 0 hour(s) and 19 minute(s) Time after: 1 mars 2013 09:19:11