I have developed an online calculator to assist with trading SPX credit spreads (Bull Put Spreads, Bear Call Spreads, Iron Condors).

I have collected 10+ years of SPX daily and intra-day data in order to analyze how the SPX moves over any time period (1 day, 5 days, 30 days, etc.). The calculator allows you to input a time period such as Friday to Friday (5 days). It then will show you how much the SPX has moved over that time period. It calculates the historical % moves and applies those %'s to the current SPX to provide the ranges.

What makes the calculator unique is I have made it so only time periods of similar volatility are extracted. I do this by using the VIX. If the VIX is currently at 13, I can have the calculator only extract the historical moves when the VIX was 15 or less (I use a slightly higher value for a cushion). This helps to greatly improve your ability to find SPX credit spreads with a balance of risk / reward.

Using this system in 2014, I have done 45 trades of a week or less. The results are 4 losers / 41 winners with a YTD return of about 125%.