Formula field based on currentdate not working

Formula field based on currentdate not working

I have this formula to calculate a person's birthday from their BirtDate (date of birth) field:

(((((((zoho.currentdate.getYear())) + "-") + (BirthDate.getMonth())) + "-") + (BirthDate.getDay())) + " 00:00:00").toDate()

Currently this is still showing dates in 2007 for most records. It only shows dates in 2008 for records that have been updated in 2008.

It seems that the formula fields are not calculated dynamically but instead are stored in the database when a record is added or updated, is this correct? Is there a way to recalculate the formula fields for all records, other than editing the formula definition? Thanks.