Based on your financial expertise, provide your response or viewpoint on the given financial question or topic. The response format is open.

What's the catch with biweekly mortgage payments?
Pete and Noah addressed the math, showing how this is, in effect, converting a 30yr to a ~23yr mortgage, at a cost, plus payment about 8% higher (1 extra payment per year). No magic there. The real issue, as I see it, is whether this is the best use of the money. Keep in mind, once you pay extra principal, which in effect is exactly what this is, it's not easy to get it back. As long as you have any mortgage at all, you have the need for liquidity, enough to pay your mortgage, tax, utilities, etc, if you find yourself between jobs or to get through any short term crisis.  I've seen people choose the "sure thing" prepayment VS the "risky" 401(k) deposit. Ignoring a match is passing up a 50% or 100% return in most cases. Too good to pass up.  2 points to add - I avoided the further tangent of the tax benefit of IRA/401(k) deposits. It's too long a discussion, today's rate for the money saved, vs the rate on withdrawal. Worth considering, but not part of my answer. The other discussion I avoid is Nicholas' thoughts on the long term market return of 10% vs today's ~4% mortgage rate. This has been debated elsewhere and morphs into a "pre-pay vs invest" question.