IB is really your only option in Aus. Government brought in rules to protect punters from themselves by not allowing margin accounts. IB had to get licensed in Aus to be able to open accounts for our peeps. Stupid really when they allow the punters to trade through cfd providers.
So, the question is about margin requirements for a Put Spread (Credit). Let's see what TradeStation says (IMO the best reference for margin & cash requirements in the retail industry): https://www.tradestation.com/pricing/options-margin-requirements/ Con1991, do you use a MarginAcct or a CashAcct in your above demonstrations? Can you say whether the requirement(s) of TradeStation is the same as TDA or IB? Or is it even different from both? FYI: with MarginAccts there are 2 requirements to meet: initial requirement (ie. when opening the position), and the maintenance requirement thereafter.