Kim, with VIX low again (around 12), the mid on the Sep20/Nov15 VIX 16 Put Calendar is around -0.50.
In previous trades you wrote (for IB) "Please note that this trade requires $150 margin per spread", which means margin for this trade should be around $150-50=$100. When I use the check margin feature in TWS it shows Initial Margin $52, Maintenance Margin $52 and it is independent of the limit price used!
How did you find this figure or information, $150 per spread?