You may not want to spend this much ($149) but I've used this program for years and have never found anything any better or even equal for the same price. Yes you can do it with an Excel spreadsheet but I have not found that to be a workable solution when tracking several loans and varying payment dates and amounts.  The software has worked fine (with only very minor glitches) on every version of windows to date. The version I have came on 3.5" disks if that will tell you something about how old it is. 

http://www.timevalue.com/products/tvalue/background.aspx?ppc=true&se=google&gclid=CLz4vrjhh6QCFctW2godYRwzIw