<prompt> Human: I have a 34k auto loan that is for 5 years at 2.85. My monthly payments are 436. I want to pay 800mo. I talked to my loan bank and they said the extra 374 could go towards either a principal-only payment or a regular payment. I asked them which way would pay off the loan faster, and they said a principle only payment. I said ok, but how is interest calculated for a regular payment. They werent able to explain it. Maybe personal finance can help me understand.Ps: I made a regular payment today and 91 went towards interest. When I make the normal payment of 436, 80 goes to interest. How is that extra 10 of interest calculated?How will making principle-only payments with the extra 374 pay off my loan faster?  <response>: Am I the only one who is confused about the math here? A quick back of the napkin puts these numbers at 600mo. Stretching out the loan for longer than 5 years, which my guess is OP is on an 84 month schedule, makes paying down the principle quicker more important. 