Share your insights or perspective on the financial matter presented in the input.

Pros/cons of borrowing money using a mortgage loan and investing it in a low-fee index fund?
Essentially, what you're describing is a leveraged investment.  As others noted, the question is how confident you can be that (a) the returns on the investment will exceed what you're paying in interest, and (b) that if you lose the bet you'll still be able to pay off the loan without severely injuring yourself.  I did essentially this when I bought my house, taking out a larger loan than necessary and leaving more money in my investments, which had been returning more than the mortgage's interest rate. I then got indecently lucky during the recession and was able to refinance down to under 4%, which I am very certain my investment will beat. I actually considered lengthening the term of the loan for that reason, or borrowing a bit more, but decided not to double down on the bet; that was my own risk-comfort threshold. Know exactly what your risks are, including secondary effects of these risks. Run the numbers to see what the likely return is. Decide whether you like the odds enough to go for it.