Okay we have two separate issues here than do converge on some level. First, yes, you are indeed correct. The Wisconsin landlord has 21 days after the end of your lease to send you either the full security deposit or an itemized list of deductions for damages above the normal wear and tear.  You must now notify the landlord of their failure to return the deposit within the 21 day period as being against the law and file a complaint with the Wisconsin Department of Agriculture. Next you have the issue of the rent.  If your agreement - lease written or oral - went until the end of the month and you did not give proper notice but just left, you are in breach of the agreement and the landlord may well be within their rights to keep the remaining 15 days.  Additionally, it may be in Wisconsin that a landlord can keep security for rent.  So if you have really breached and not given proper notice and just left the lease, they again may be in the right.  Seek help from a tenant's rights organization or an attorney in your area.  Good luck.