In this paper, five different types of amortization plans with constant instalments are analyzed with a unified approach: a pair of plans in simple interest regime, a pair of plans in compound interest regime and a plan in a hybrid context. In the two pairs there are a main plan and an auxiliary one. Here we give a comprehensive discussion of all the rules governing these plans, showing similarities and differences. Furthermore, the pair of plans in simple interest regime is at the origin of the hybrid plan, which surprisingly turns out to be a (main) plan in compound regime with variable instalments.
