Simple interest calculator

Simple interest is the flat kind: principal times rate times time, charged once, never snowballing. The day-count basis only matters for day-based terms, and the banker's 360 is a convention that quietly pays a little more interest than actual/365 on the same deal. The comparison line compounds the same principal yearly at the same rate so you can see the gap; most real loans compound monthly, which drifts higher still. What it does not do: fees, penalties, part-period payments, amortisation schedules, or tax. Back-solving assumes the given interest is plain simple interest, not a compounded figure.