Formula for Vacation Days when eligible

I am looking for a formula that will calculate the date when their vacation is due.

Ex. Employee is eligible for 10 days vacation after 1 year of employment, 15 days after 5 years years and 20 days after 10 years.

Emp #1 - Hired on 05/11/12, his vacation would not be due until 05/11/13 and he would have 10 days put in his "bank". At any given time when I open the spreadsheet I need to see what employees have vacation days due.

So if I opened this spreadsheet on 05/09/13, there were not be 10 days in his vacation "bank", but if I opened the spreadsheet on or after 05/11/13, there would be 10 days in his vacation "bank".

I hope that makes sense.

Thank you.

Works perfectly thank you so much for your quick response!!!!!