<prompt> Human: I need to pay for a degree program. The cost is 12,000 up front. I can get a 0 credit card with no payments for 21 months. I could pay it off in installments. Alternatively, I could invest what my payment would be every month in a vanguard index fund and pay it off early. Should I do this? Whywhy not?  <response>: Because in 21 months if the market crashes 20 you wont have the money to pay the balance before the interest kicks in.Alternatively you could just put it in a high-interest savings account, though at 1 interest you will only make 100 depositing 21 payments of 571So in answer to your question, you should never invest money that has a strict timeframe... you dont want to be pulling out at the bottom of the market... and with a fixed timeline you wont have a choice. 