Calculating the number of days between two dates

[hacktek]

I have a mySQL database.I need to count the number of days between two dates.My client is going to fill an input ("hm_date") with January 1, 1979 via php form to create a new record.I need a field ("total_days") to calculate the total number of days from "hm_date" to the present day. I need this field to always update itself with each passing day.How do I make "hm_date" appear with total days and is always updated?I'm assuming this is achieved server-side?Should I use strototime() ?Erik