ROI calculator
A 50% return sounds identical whether it took one year or ten, and it is not remotely the same investment. Annualised, one year at 50% is 50% a year; ten years at 50% is 4.1% a year; below inflation for much of the last decade. Any comparison of returns over different holding periods that does not annualise first is comparing nothing at all.
Past returns say nothing about future ones. This is arithmetic on figures you supply, not investment advice.
ROI is profit divided by cost. Turning 10,000 into 15,000 is a 50% return; spread over three years that annualises to 14.5% a year. Always annualise before comparing investments held for different lengths of time.
How to calculate ROI
Simple ROI ignores two things that usually matter. The first is timing: money returned early can be reinvested, which is why internal rate of return exists as a more rigorous measure for uneven cash flows. The second is what else you could have done with the money; a 6% return is excellent against cash and poor against a broad equity index over the same period. Neither of those makes ROI useless; they make it the beginning of an analysis rather than the end.
Questions
Subtract cost from final value, divide by cost, multiply by 100.
The constant yearly rate that would produce the same total return. It is the only fair basis for comparing different holding periods.
Yes. Add transaction costs and ongoing fees to the invested figure, or the return is flattered.
It depends on risk and alternatives. Compare against what the same money could have done elsewhere over the same period.
ROI ignores when cash arrives; IRR accounts for the timing of every flow and is the better measure for uneven ones.