I keep having trouble with this simple calculation! So, here is a little example to get the amount of days between now and the next occurance of July 1st.

//set up the 2 date objects
$now = new Zend_Date();
$next = new Zend_Date();
//we want July 1st
$next->setDay(1)->setMonth(7);
//if we are currently after july this year
if ($now->get(Zend_Date::MONTH) >= 7) {
    //we need to work it out til next July
    $next->setYear($now->get(Zend_Date::YEAR) + 1);
}
else {
    //this july is fine
    $next->setYear($now->get(Zend_Date::YEAR));
}
$diff = $next->sub($now)->toValue();
return $diff / 60 / 60 / 24;