Am I simplifying things too much?  If you get a set amount of leave, lump sum, on your anniversary date -- based on amt of time with company - then why not just say that as of Jan everyone gets their leave and they have until next Jan to use it?  Starting with the first month of the year ensures that everyone gets their leave that year, not missing anyone.  Even if you got your leave balance say in Aug 03, and they implemented this in Jan '04, you would have what you had from '03 + the new balance for '04.  All that leave would have to be used by Jan 05.  They could even do a bit more work and say that for '03 you had xx # of hours/days that must be used NLT Aug '04, with the remainder able to be taken all the way through to Jan '04.  Then those who are already getting leave as of Jan wouldn't be adversly affected since they're basically on that schedule.  Those who use Feb or Mar will have already used most of their leave and won't have a lot of carry-over, but will not be punished by switching over, and those who get their leave in Dec under the old system still get their leave too, but are switched over to the new system too.  It might appear that they're getting double the leave, but they're not, just moving their next leave accrual date back from Dec to Jan.

CountriGal
Peer Moderator