[quote=Essbee]Hmm, but if you pay now, and the extra goes toward principal, doesn’t a larger proportion of your January and February payments go toward interest instead of principal? (ie because the remaining principal is less) on the date that those bills are generated?[/quote]

It’s the other way around. If your outstanding principal is less, interest computed is on a lower principal. Your monthly payment remains the same, but a a larger portion of it goes to principal instead of interest payments. If in doubt, just go use a decent amortization calculator.