I want to find a calculator where between any two dates provided, the return on a given amount of money is calculated for the actual returns of the S&P 500 between those dates.
MoneyChimp is great for this. It only offers full year returns, but it compounds the results correctly, including dividends. For mid year results, just adjust a bit based on the data you can find from Google or Yahoo to add some return (or loss) for the months.
Well i dont know of any calculator but you can do the following
1) Google S&P 500 chart
2) Find out whats the S&P index points (P1) on the first date
3) Find out whats the S&P index points (P2) on the second date
4) P1 - P2 = result
returns in % = result / P1 * 100