ROI Solver works with any scenario possible, and it is easy to use.
Hand held financial calculators, such the HP 12C, only works with specific events. It will give the ROI (interest rate) if three of these four numbers are known: number of periods, present value, payment per period, or future value. In other words, every transaction has to be for the exact same amount of money for every period, and every time period must occur at regular intervals, such as monthly or annually. Real life investments rarely fit this.