Over the years, there have been quite a few questions about interest only loans, and quite a few mistaken answers. A user in the Quicken Forums said: "I can find no way to have quicken calculate "interest only" payments. It shows P&I What am I missing?" Two other users answered that "question" and suggested that Quicken could not handle "interest only" loans.
Quicken's Loan Wizard can, indeed, handle "interest only" loans. You set them up pretty much like any other loan, with two exceptions: you must Quicken there is a "balloon payment" at the end of the loan; and you must enter the "exact" amount of the payment (the exact amount of the interest
[If you do not know the payment amount (not sure why this would ever be), you can get around the problem by entering almost any payment amount, completing the loan setup process, then looking at the Quicken loan "Payment Schedule" and noting the amount of interest for the very first payment. If you then modify the loan and change its payment amount to the amount of the interest from that first payment, you should find the principal amount for all payments goes to zero and the full amount of the loan is shown as a balloon payment following the last interest only payment.]