In short, I believe that if you have a $300,000 home with a $150,000 mortgage, it is, in general, better to have a 'stache of $850,000 and continue to pay down the mortgage at the normal rate than to pay off the mortgage and have a 'stache of $700,000.
I've been around this debate for nearly a decade. I agree with both the rational Vulcan-logic approach (get a 400-year mortgage) as well as the
emotional investor behavioral psychology approach (sleep better at night through less risk). If your risk tolerance is such that you're not likely to follow through on 30 years of mortgage payments then you should absolutely pay it off early. Otherwise you're just wasting your money on interest & closing costs.
Those who claim the superiority of either approach are missing the point: different tactics for different people. There's more than one way to FI, and different people will tolerate different levels of risk. Asking someone to exceed their risk tolerance is begging for failure, no matter how compelling the math or logic. Emotions triumph over math & logic every time, and I doubt that can be changed. If it could then everyone would be eat healthy, exercise, and be happy-- and a whole bunch of behavioral psychologists would be unemployed.
However this thread can add a few analysis aspects.
First, if you're going to leverage up with a mortgage, then it makes no sense to have anything else in your investment portfolio which yields less (after tax) than the mortgage (after tax) interest. For most investors this means getting rid of short-term bonds, TIPS, I bonds, and all sorts of CDs. It's probably best to maintain a portfolio with no bonds and only 1-2 years of cash to cover expenses during a bear market. Good luck with that, but if you think having a mortgage is a good idea then you also probably think that you're ready to tolerate the enhanced volatility of the rest of your portfolio. Very few people have the brass-plated cojones for this. By the way that brass plating wears mighty thin after 30 years or by the second recession, whichever comes first.
Second, run both scenarios (mortgage vs no mortgage) through FIRECalc or a Monte Carlo calculator. (Let's not get distracted by calculator weaknesses/flaws. I know they suck, but that's beside the point.) See how your failure rates change. A larger portfolio (with a mortgage payment) may be more survivable than a smaller portfolio (without a mortgage payment). It depends on how badly the portfolio gets hammered by that series-of-returns issue, the size of the portfolio, and the size of the mortgage balance. The calculator flaws may cancel each other out through their relative results, but I haven't done the research to verify that.
Third, I think that people with reliable inflation-adjusted annuity income should absolutely have a mortgage. Even people with fixed annuities may benefit from having a mortgage. If you're confident that you'll have money coming in each month then you can cover your mortgage payment no matter how much the sequence of returns sucks. By "reliable", I mean military retirees. (Municipality civil-service retirees and retired airline pilots... not so much.) Of course I'd also recommend against scampering out to get an inflation-adjusted annuity just so that you can get a mortgage next. That works against you with expenses & fees. But military retirees already have their COLA'd pension for other reasons, so they might as well exploit it.
Fourth, don't count on the tax deduction unless you itemize other deductions as well (like huge medical expenses or charitable contributions). Even with a jumbo mortgage, about 20 years into the 30-year term the annual interest payment drops below most itemized deduction thresholds.
Fifth, here's a thread that I've been running for over eight years on the subject, including reactions to the 2008-09 bear market:
http://www.early-retirement.org/forums/f28/covering-a-mortgage-without-losing-your-ass-ets-15237.htmlI update it every six months or so.
Having said all of that, spouse and I have 30-year fixed mortgages on both our home (3.625%) and our rental property (4.625%). Our investment portfolio has no bonds and over 85% equities. (We're slowly spending down our cash to get it back up to ~92% equities.) Our FIRECalc success ratio is 67% just on the mortgage arbitrage alone, which of course implies that the failure rate is 33%. Our mortgages are over 15% of the size of our portfolio, though, so our total portfolio's survival rate climbs by a few percentage points from 95% to 99%. The mortgage payments (P&I) amount to over two-thirds of my military pension, so I still have money left over for groceries & utilities. We handily beat the itemized deduction threshold because Hawaii real estate is expensive and they're honkin' big mortgages.
Even at a 30-year fixed mortgage interest rate of 5.375% (the original rate) we're currently "winning". At our latest mortgage's interest rate of 3.625% we're just running up the score. However during the Great Recession we were testing our emotional tolerance for sequence-of-returns volatility. It was not much fun.
When we first took out the rental mortgage in late 2001, we put all of the money into Berkshire Hathaway "B" shares because I felt that they were undervalued. It worked out so well that I doubt I'll ever duplicate its success in my lifetime. (We put our residence mortgage money into the iShares S&P600 small-cap value ETF (IJS)). We've kept restarting the mortgage clock with each refinance, so today's mortgages will be paid off in 2040-- when I'm 80 years old.