It also depends on the term of the loan, and will change as interest rates change. The optimal point is currently $75 only for a very narrow number of loans: grades A1 - B2, 36-month loans. Basically, you need to calculate the monthly payment for each investment value, then determine the value that gives a payment closest to ending in 49 cents without going over. If no such value exists, then use the highest cents to minimize the amount of rounding loss.

I agree with Josh, that the tiny amount saved isn't worth the loss of diversification, but just for the sake of curiosity, attached are charts showing the optimal rounding ranges for notes up to $100.

Sean

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