Extra cash - go towards mortgage, or stock?
It's six of one a half dozen of another.   Investing the cash is a little more risky.  You know exactly what you'll get by paying down your mortgage.  If you have a solid emergency fund it's probably most advisable to pay down your mortgage.   If your mortgage is 3% and your investment makes 3.5% you're talking about a taxable gain of 0.5% on the additional cash.  Is that worth it to you? Sure, the S&P has been on a tear but remember, past results are not a guarantee of future performance.