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(Me writing to support)
Dear Mr. XXXXX,
just a final question:
what is the basis for PnL% calculation for such a CashSecuredPut trade? Ie. the invested amount?
Is it the StrikePrice or "StrikePrice minus PremiumReceived"?
I just mean this mathematical basis.
And are you aware of the fact that other brokerage firms use this CashRequirement formula for such CashSecuredPut (aka CashCoveredPut):
(StrikePrice x Multiplier x Contracts) - PremiumProceeds
Cf.
https://www.tradestation.com/pricing/options-margin-requirements/
Whereas you (TD) seems to use this:
(StrikePrice x Multiplier x Contracts)
There is obviously a big difference.
Thank You.
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(Support replying to my above webmail, but not Mr XXXXX but now a Mr. YYYYY
)
Thank you for your email, I hope you are having a wonderful evening. My name is YYYYY and I would be more than happy to assist you.
Our policy is maintenance requirement for a cash secured put is: Cash to cover the exercise value of the option (strike price x number of contracts x multiplier)
Any premium received will certainly be used when calculating option buying power effect. But the margin requirement will need to include the entire amount of the assignment. The basis for not including the premium in the margin requirement is because if you do get assigned your cash-secured put, you will need the entire amount of the assignment available to facilitate your obligation of the assignment.
I hope this helps. Should you have any further questions or concerns, please do not hesitate to reach back out to us.
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Q1: Can anybody decipher what this support guy tries to say?
He even is talking of "margin" 
Q2: Has my question really deserved such an unqualified answer by such a clueless support?