Michelle,

Please note that that’s a VERY big ‘if’ in the short-term.

Historically, diversified groupings of stocks (such as the S&P 500) return about 7% after costs, but it’s very uncertain whether the outstanding returns over the past ~9 years will continue in the near future. Some people are predicting an impending drop in the stock market. It’s unknowable whether their predictions that it’ll happen this year are correct, but the fact is that a correction is coming.

Therefore, I’d advise paying down the mortgage in the near-term. Eliminate debt, in order to minimize the regret if you end up investing just before a bubble bursts, and in order to maximize your ability to take risks. It’s worth reading this: http://jlcollinsnh.com/2011/06/06/why-you-need-f-you-money/ or watching this video that’s definitely NOT for little ears: http://jlcollinsnh.com/2016/03/19/f-you-money-john-goodman-v-jlcollinsnh/

The point here is that, once your house is paid off, you’re in that “F-You” position and can afford to take such risks as sinking all available dollars into investments. That way, you don’t have to worry about a market downturn–there’s no debt to pay off with that money anyway, so you can focus on the long-term and ignore short-term corrections.

Here’s the bottom line. You could:
1) Invest a bit (up to an employer’s 501k match, for example) and put the rest of the money toward paying off the mortgage early,
or 2) Pay the minimum mortgage payment and aggressively put the rest of the money toward investments.

The worst-case scenario in #1 is that the stock market drops and you lose a bit of money, but at least your home is getting paid off early! The worst-case scenario in #2 is that the stock market drops and you lose a whole lot of money, AND your home is not on track to get paid off early.

I believe that you should have long-term faith in the stock market. But you should be wary about picking NOW to start investing.