Lesson 13 of 20 · 7 min
Margin requirements on short options
Writing an option ties up capital sized to the obligation, and the amount changes as the market moves.
A long option is paid for in full and requires nothing further. A short option is different: the writer received cash and accepted an obligation, so the broker requires collateral against the possibility that the obligation becomes expensive.
The requirement is not the premium received. It is computed from formulas that scale with the underlying's price and the option's moneyness, or in more sophisticated systems from a risk model that stresses the position across a range of price and volatility scenarios. Either way the number is far larger than the premium, and — this is the part that matters — it is recalculated continuously.
That recalculation is the mechanism people miss. As the underlying moves against a short option, two things happen at once: the position loses money, and the collateral required to hold it increases. The loss and the demand for cash arrive together, from the same cause. If the account cannot meet the increased requirement, the broker can require a deposit or close positions, choosing which ones.
The structural parallel with Track 1 is exact. A maintenance threshold on a pledged portfolio and a margin requirement on a short option are the same kind of object: a continuously computed test that tightens under stress and whose breach transfers the choice of what to sell from you to someone else. Recognising the pattern once means recognising it everywhere.
Key terms
- Initial and maintenance requirement
- The collateral needed to open a short option position, and the amount that must be maintained afterwards.
- Risk-based margin
- A requirement computed by stressing the whole position across price and volatility scenarios rather than by a fixed formula.
- Buying power
- Capital available for new positions. A short option consumes it in the amount of its requirement, not its premium.
Worked example
A $200 premium and a growing collateral demand
One short $50 put, premium $2.00, stock at $50. Requirement illustratively 20% of the underlying value less the amount out of the money.
- Premium received
- $200
- Requirement at $50
- about $1,000
- Stock falls to $44 — position value
- Loss of roughly $400
- Requirement at $44
- about $1,480
- Change in cash needed
- Up about $480
20% × $5,000.
Deeper in the money, larger requirement.
While the position is down $400.
The position lost $400 and simultaneously demanded $480 more collateral. Both movements came from the same price change. Illustrative formula.
Check yourself
You write one put and collect $200. Why does the position consume far more than $200 of capital, and what happens to the requirement if the underlying falls?
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Educational only. Nothing in this lesson is investment, legal or tax advice, or a recommendation to enter into any transaction. Figures are illustrative and computed from the inputs stated in the lesson.