Mid month lease, a rookie mistake

[Irma Siney]

Last year a tenant signed a lease contract that started January 15, and for some reason, may be a senior moment, I wrote the contract to end this year on January 15. (He paid deposit + last half of January to move in) Mid December the tenant notified me he was moving out when the lease ended, but when January came around he did not make any payments. I contacted him and asked if he was moving the beginning or end of January, he replied the 15th. My question is, shouldn't he need to pay for half of January since that's when the contract ended? When he asked about his deposit I told him I deducted half of January and gave him the difference back. He did not like this at all and said he's taking me to court.