How to calculate the rate of return on selling a stock?
You probably want the Internal Rate of Return (IRR), see http://en.wikipedia.org/wiki/Internal_rate_of_return which is the compound interest rate that would produce your return. You can compute it in a spreadsheet with XIRR(), I made an example: https://spreadsheets.google.com/ccc?key=0AvuTW2HtDQfYdEsxVlM0RFdrRk1QS1hoNURxZkVFN3c&hl=en You can also use a financial calculator, or there are probably lots of web-based calculators such as the ones people have mentioned.