As a month to month tenant, you will need to give your landlord 30 days notice that you intend to move. At the conclusion of the 30 days, when you move out, your landlord will have 15 days to return your security deposit or 30 days to send you a certified notice explaining why he is keeping any part of your security deposit. As for the last month's rent, once you provide notice of your intent to move, discuss with your landlord that he already has your last month rent payment.
In most states, security deposits can only be held for unpaid rent or damage beyond normal wear and tear done to the premises during your residence. If your lease expired, you are now a month to month tenant which means that you are not obligated long-term. In most states, as a month to month tenant, you only have to give 30 days' written notice (it may be different in Florida) that you desire to end your tenancy.
Your local laws should dictate the instances in which a landlord can hold a security deposit. The following website may provide you with some helpful information:
DISCLAIMER: Brandy A. Peeples is licensed to practice law in the State of Maryland. This answer is being provided for informational purposes only and the laws of your jurisdiction may differ. This answer based on general legal principles and is not intended for the purpose of providing specific legal advice or opinions. Under no circumstances does this answer constitute the establishment of an attorney-client relationship. For legal advice relating to your specific situation, I strongly urge you to consult with an attorney in your area. NO COMMUNICATIONS WITH ME ARE TO BE CONSTRUED AS ARISING FROM AN ATTORNEY-CLIENT RELATIONSHIP AND NO ATTORNEY-CLIENT RELATIONSHIP WILL BE ESTABLISHED WITH ME UNLESS I HAVE EXPRESSLY AGREED TO UNDERTAKE YOUR REPRESENTATION, WHICH INCLUDES THE EXECUTION OF A WRITTEN AGREEMENT OF RETAINER.
Actually, you only need to give 15 days notice pursuant to Florida statute section 83.57. The last month's rent is for the last month's rent. Make sure that you provide your landlord with your forwarding address and take lots of pictures. If the landlord is late in providing your notice you may want to seek counsel to get your security deposit back.
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Read your written lease agreement that has expired.
See if it has any language about clauses or the entire agreement surviving the expiration except that it just becomes a month-to-month.
Some leases expire and become month-to-month.
Some leases expire as far as the term (annually or whatever) goes but all of the other clauses survive.
If no clauses survive that speak to termination notice after expiration,
then statutory law applies and you will have to give 15 days' written notice so that the landlord receives the notice by certified mail at least 15 days before the next rent is due.
If the clauses survive, see if more time than 15 days is called for.
Once you give proper notice that you are leaving, the landlord should apply the last month deposit to your account.
Before you move, remove your items, clean thoroughly, and take lots of pictures.
Ask for a walk-through if possible and hand the landlord the keys.
Include your forwarding address in the termination letter if you can.
If you can't , then send a certified letter to the landlord as soon as you know the forwarding address or the day you move.