Landlord refuses to refund deposit

My previous landlord has refused to refund my deposit because they claim I did not give 30 days notice (I did). I plan to take them to small claims court but I understand that I can claim interest on the deposit for the length of my residence. How do I calculate the interest?

Your state probably has a formula that they use to calculate interest in this kind of situation. Try and find out the answer from the city attorney's office or a tenant's rights organization.