Leave Accrual Spread sheet

Hi

I am creating a spreadsheet that check employees employment date and
calculates how much sick leave,Annual Leave and Study Leave they have.
How its calculated is that an employee gets 10 days of sick leave per year which accumulates
for 3 years so for a 3 year period its 30 days and then resets back to 0 days after a 3 year cycle.
Annual leave is 17 days per year which accumulates and does not fall away. Study leave its 5 days
per year and falls away every year. The year is calculated on date of employment so if you are employed on 10/02/2012
your year ends at 10/02/2013 (365 Days later). Please can you assist with a macro to calculate this.