Hi SF When you first sell a put you need to have the cash sitting around to actually take delivery So I would use that as the starting date. So if you took in $1 you actually need $19 to back up the $20 put. 1/19 = 5.2% return over 90 days or 21% annualized ( 5.2 x 4 ) If you then sell a $20 call and have it called you made ( roughly ) 2 / 18 = 11.1 % or 22.2% annualized Or you made 1/19 = 5.2 % then 1/18 = 5.6% so 5.2 + 5.6 = 10.8 % x 2 = 21.6% annualized That's my thought. Toofuzzy