FICO 08 really likes to see a mix of open revolving and installment loans. An open installment loan will slowly build your score as you make payments and the balance goes down. However, you will loose most (but not all) of the score benefit once you pay off your last open installment loan. I would expect a 20-30 point drop once the last loan is paid off. Of course, it will vary depending on your credit report how much your score drops.
Mortgages don't use FICO 08 scores. They use FICO 04/98 scores. I don't believe the older models penalize you as much for not having both open installment and open revolving credit lines. However, I think it is still good advice to have one almost paid off installment loan to maximize your FICO 04/98 scores. For most people that would be a car loan or current mortgage. If you do not have any other installment loans, the cheapest way to get one is a $500 shared secured installment loan. It may not impress an underwriter. But if it boost your middle FICO 04/98 score over 760 (or other boundary score), it will likely reduce the interest rate for the loan.
