Quote from YIELDSAFE:
Trade #5 (opened on 10/18/11)
Sold TLT Nov 19 2011 108.0 Put @ 0.90
Bought TLT Nov 19 2011 106.0 Put @ 0.58
Net Credit of 0.32
Trade #5 (closed on 11/1/11)
Bought TLT Nov 19 2011 108.0 Put @ 0.29
Sold TLT Nov 19 2011 106.0 Put @ 0.17
Net Debit of 0.12
Return = 0.20 (original credit of 0.32 minus debit of 0.12)
Return% = 0.20 / 1.68 = 11.90%