Margin at 9% equals paying 0.025% per day. July 149 SPY Calls Ask: $4.40 have an theta (time decay) of: -0.031 This equals losing 0.70% per day, 28 times margin. Which means: Options writers have an edge over buyers. If you buy options, buy them on margin, preferably portfolio margin. You get more leverage, losing less as time passes. It's not surprising 90% of options expire worthless.