Interest and APR: a short explainer

I needed recently to check the monthly payment amount for a simple loan; choosing four online loan calculators at random, I got two slightly different values. In this PDF document Interest rates & APR (v0.1), I’ve detailed the differences (spoiler: it’s due to APR) and shown how the figures from the online calculators were arrived at. As ever, I hope someone finds it useful!

A plea: If you know of any book that goes into the various types of loan scheme in some depth, in a fairly formal and systematic way, please do let me know; it’s an area I find fascinating, yet there doesn’t seem to be a single definitive online resource with quite enough depth.

Finally, I must sing the praises of Wolfram Alpha, it’s been invaluable for my work for the past couple of years. Between Wolfram Alpha, wxMaxima and R, they’ve been able to solve any equation I’ve had cause to throw at them!