Query: Paying Off Principal of Home vs. Investing In Mutual Fund

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 <=SEP=> Excellent answers so far, so I will just add one additional consideration: liquidity. Money invested in a mutual fund (exclusive of retirement accounts with early withdrawal penalties) has a relatively high liquidity. Whereas excess equity in your home from paying down early has very low liquidity. To put it simply: If you get in a desperate situation (long term unemployment) it is better to have to cash in a mutual fund than try to sell your house on the quick and move in with your mother. Liquidity becomes less of an issue if you also manage to fund a decent sized rainy-day fund (6-9 months of living expenses).

 <=SEP=> Naturally the advice from JoeTaxpayer and dsimcha is correct, every situation is different.  I will get reckless, go nuts and make a recommendation! You are young, childless for the time being.  Do the following with your money: ALTERNATE IDEA for #6 Fix yourself up for the long term first, then have a bit of fun, then get out of the house debt.  In that order.

 <=SEP=> "I was going to ask, ""Do you feel lucky, punk?"" but then it occurred to me that the film this quote came from, Dirty Harry, starring Clint Eastwood, is 43 years old.  And yet, the question remains. The stock market, as measured by the S&P has returned 9.67%  compounded over the last 100 years. But with a standard deviation just under 20%, there are years when you'll do better and years you'll lose. And I'd not ignore the last decade which was pretty bad, a loss for the decade.  There are clearly two schools of thought. One says that no one ever lost sleep over not having a mortgage payment. The other school states that at the very beginning, you have a long investing horizon, and the chances are very good that the 30 years to come will bring a return north of 6%. The two decades prior to the last were so good that these past 30 years were still pretty good, 11.39% compounded.  There is no right or wrong here. My gut says fund your retirement accounts to the maximum. Build your emergency fund. You see, if you pay down your mortgage, but lose your job, you'll still need to make those payments. Once you build your security, think of the mortgage as the cash side of your investing, i.e. focus less on the relatively low rate of return (4.3%) and more on the eventual result, once paid, your cash flow goes up nicely.   Edit - in light of the extra information you provided, your profile reads that you have a high risk tolerance. Low overhead, no dependents, and secure employment combine to lead me to this conclusion. At 23, I'd not be investing at 4.3%. I'd learn how to invest in a way I was comfortable with, and take it from there.  Disclosure (Updated) - I am older, and am semi-retired. I still have some time left on the mortgage, but it doesn't bother me, not at 3.5%. I also have a 16 year old to put through college but her college account i fully funded."

 <=SEP=> I wouldn't pay down your mortgage faster until you have a huge emergency fund.  Like two years' worth of expenses.  Once you put extra money toward principal you can't get it out unless you get a HELOC, which costs money.  You're in a position now to build that up in a hurry.  I suggest you do so. Your mortgage is excellent.  In the land of inflation it gets easier and easier to make that fixed-dollar payment: depreciating dollars. You seem like a go-getter.  Once you have your huge emergency fund, why not buy a few websites and monetize the heck out of them?  Or look for an investment property from someone who needs to sell desperately? Get a cushion that you can do something with.

 <=SEP=> Paying off the debt is low-risk, low-reward.  You're effectively guaranteed a 4% return.  If you buy a mutual fund, you're going to have to take some risk to have a decent chance of getting better than 4% and change return in the long run, which probably means a fund that invests primarily in stocks.  Buying a stock mutual fund is high-risk, high reward, especially when you're in significant debt.  On the other hand, 4% and change is very low-interest.  If you wanted to buy stocks on margin, financing stock investments directly with debt, you'd pay a heck of a lot more.  Bottom line:  It comes down to your personal risk tolerance.

 <=SEP=> Other answers are already very good, but I'd like to add one step before taking the advice of the other answers... If you still can, switch to a 15 year mortgage, and figure out what percentage of your take-home pay the new payment is.  This is the position taken by Dave Ramsey*, and I believe this will give you a better base from which to launch your other goals for two reasons: Since you are then paying it off faster at a base payment, you may then want to take MrChrister's advice but put all extra income toward investments, feeling secure that your house will be paid off much sooner anyway (and at a lower interest rate). * Dave's advice isn't for everyone, because he takes a very long-term view.  However, in the long-term, it is great advice.  See  here for more. JoeTaxpayer is right, you will not see anything near guaranteed yearly rates in mutual funds, so make sure they are part of a long-term investing plan. You are not investing your time in learning the short-term stock game, so stay away from it.  As long as you are continuing to learn in your own career, you should see very good short-term gains there anyway.

 <=SEP=> The mathematically correct answer is to invest, because you'll get a higher rate of return. I think that answer is bunk -- owning your home free and clear is a huge burden lifted off of your shoulders. You're at an age where you may find a new job, business, personal or other opportunities will be easier to take advantage of without that burden.

 <=SEP=> "I'm probably going to get a bunch of downvotes for this, but here's my not-very-popular point of view: I think many times we tend to shoot ourselves in the foot by trying to get too clever with our money. In all our cleverness, we forget a few basic rules about how money works: It's better to have 0 debt and a small amount of savings than lots of debt and lots of savings. Debt will bite you. Many times even the ""good"" mortgage debt will bite you. I have several friends who have gotten mortgages only to find out they had to move long before they were able to pay it off. And they weren't able to sell their homes or they sold at a loss. When you have debt, you are restricted. Someone else is always holding something over your head. You're bound to it. Pay it off ASAP (within reason) while putting a decent amount into a high-yield savings account. Only after the debt is gone, go and be clever with your money."