Chicago Two Flat Security Deposit Question

[Jimmy M.]

Quick Question for the BP Team:

- We purchased a two-flat in April, and we are owner-occupying one unit, renting the other.  The other unit was rented when we took possession.  His lease went until October 31st, 2019 (yesterday).  He has renewed on our lease starting from today until May 2021 (he's a great tenant).  

- I'm holding the same security deposit I got at closing in April.  Now that the new lease has started do I pay him interest on that from April to October (0.01% for Illinois)?

- Do I do this at the end of every year?

- Am I exempt from this because the law only calls out 25 units for this? 

I figured someone would know these things pretty quickly here.  The law is somewhat vague.