Here is a simple calculator to assist you in figuring out what interest you should be using when you bid on a listing. It takes into account the borrower credit grade and your desired interest rate. This tool calculates the adjusted interest rate which accounts for the Prosper loan servicing fee and the average default rate for borrowers with the same credit grade. Please note that actual results may vary.
Update: Prosper now has a risk calculator that will estimate your earnings based on the historical performance of similar listings in the past when making your bid. I highly recommend utilizing this tool when bidding as it is more accurate.
You may also be interested in reading the following posts:
