Margin charged on a spread as a package rather than leg by leg, which is why a defined-risk structure requires only its maximum loss.
Brokers recognise that the long leg of a vertical caps the short leg's risk, so they charge the width minus the credit rather than a naked-option-requirement. The recognition depends on the legs being in the same underlying, the same expiration and correctly paired — which is a matter of how the order was entered.
This is where legging into spreads causes real damage. Two separately entered orders may sit in the account as a naked short and an unrelated long, carrying full naked margin until the broker's overnight process pairs them, and sometimes not even then.
Example: the XYZ $47.50/$45 put spread requires $190. Sell the $47.50 put alone and you face roughly $900 of naked-put requirement until the $45 put is bought and the pair is recognised. Same final position, very different intraday capital.
Original diagrams for the ideas on this page. Illustrative, not real market data.
Margin and leverage. A $5,000 deposit can control a $100,000 position, which is 20:1 leverage. Because the loss is measured on the full $100,000, a 2.5% move against you halves the deposit and brings a margin call, and a 5% move uses all of it.
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