A family friend lent my wife money years ago, before we got married. I am paying him back although I don't think he ever expected to see the money again. I feel like he deserves interest, perhaps a high rate since he did not know if he would see it again. Then again, I am sure he also did not expect to get much if any interest either. Given that I can afford to fully repay with interest, what seems fair?
I was thinking of applying a 10Y rate which is 1.75-4.8% over the period covered.