A biweekly payment plan doesn't ask you to pay more each month — it just splits your normal monthly payment in half and collects it every two weeks instead of once a month. The trick is in the calendar: there are 52 weeks in a year, which means 26 half-payments — the equivalent of 13 full monthly payments instead of 12.
That extra payment happens automatically, once a year, without you ever having to decide to send more money. Applied entirely to principal, it has the same compounding effect as a lump-sum extra payment: it shrinks the balance interest gets calculated on, a little more each year, which adds up to years off a 30-year loan and real interest savings over the life of it.
One thing worth checking before switching: some lenders charge a setup fee for a formal biweekly program, or apply payments differently than a true biweekly schedule. If that's the case for your loan, you can often get the identical effect for free by simply adding 1/12th of your payment to what you send each month — same math, no program required.