I had a car loan one time on which I made extra payments on the principal. The first time I did it they did consider it as an advance payment. The reason was that I sent it from my bank to them and they transferred it electronically and the loan bank's computer didn't know any better. The bank fixed the problem but all future principal payments had to be made by check and it had to have the "Principal Payment Only" written on the check memo field. That way it was handled manually and no more problems with the payments being considered advance payments. YMMV