When analyzing potential spread trades I like to use Online Options Profit Calculator http://www.optionsprofitcalculator.com/calculator/iron-condor.html as my broker's calculator is not very good, but I've noticed problems with it. E.g., theta (time decay) on weekend days are shown as if they are equivalent to weekdays; and while there should be more decay over a weekend than overnight, weekend gaps versus daily overnight gaps are not so much greater as to justify two full days and night's worth of theta - I wouldn't think it's equivalent to even a single day's worth of decay, and my experience seems to bear this out. The example in the link shows an enormous time decay of $158 over the coming 3 day weekend. Does anyone here have any rule of thumb for estimating what it really should be and how to adjust the expected decay for the subsequent days that are also affected by this initial distortion? Are there better calculators which adjust for this difference in theta for times when the market is closed?