I've been flicking through the comments looking for some succinct date code and have noticed an alarming number of questions and over-burdened examples related to date mathematics.One of the most useful skills you can utilize when performing date math is taking full advantage of the UNIX timestamp.The UNIX timestamp was built for this kind of work.
An example of this relates to a comment made by james at bandit-dot-co-dot-en-zed.James was looking for a way to calculate the number of days which have passed since a certain date.Rather than using mktime() and a loop,James can subtract the current timestamp from the timestamp of the date in question and divide that by the number of seconds in a day: