Note that the source of 99% of errors in financial calculations stems from not having your interest match your compounding correctly as specified. Make sure you are doing that correct, and the rest is easy!
I always tell finance students - learn how to interpret interest and compounding correctly before anything else and REALLY understand it. That will make the course simple.
Although I work for the HP calculator group as a head developer of the HP Prime, the views and opinions I post here are my own.