<prompt> Human: Hello rpersonalfinance,I recently closed on my first home and have been contemplating the best method to pay off my mortgage early.Mortgage details: Type: 30 Year Conventional Amount: 252,000 Interest Rate: 2.375 fixed Monthly payment interest principal: 980 Total interest paid after 30 years: 100,584Initially I was crunching the numbers to figure out what the extra payments to principal would be monthly or annually to pay it off in 15 years.For anyone curious:Additional monthly principal payment Monthly payment amount: 1,665.53 per month 686.12 monthly increase Interest saved: 52,791.37 Total interest paid after 15 years: 47,793.45Additional yearly principal payment Annual payment amount first of the year: 8,144.48 annually Interest saved: 54,123.98 Total interest paid after 15 years: 46,460.84So paying the mortgage off early via payments to principal will save me roughly 50k in interest over 15 years.After thinking about it some more I began to wonder if I should instead take the money I would make towards the extra principal payments and invest it in index funds. Given the relatively low interest rate on my mortgage I only need to make an average return of 3 over 15 years to come out ahead.I know past performance is no indication of future performance but the 10-year total return on SPY for example is well over 3. Granted the markets have been in quite the upswing the last decade or so. Is this a sound strategy? Thoughts?  <response>: Your interest rate is 2.375 fixed? Theres no way Id pay a penny extra on that payment - thats well below the threshold where Id rather invest. 