Margin and Buying Power for Options
One of the first surprises new options sellers hit is buying power: you sell a single put for $80 of premium and your broker reserves $2,000 of capital. Understanding how margin and buying power work for options tells you how much you can actually trade — and stops a margin call from forcing you out at the worst moment.
Open the Cash Secured Put calculator →Buying power vs the premium you collect
Buying long options is simple: you pay the premium in full and that is your maximum loss, so the buying power reduction equals the cost. Selling options is where capital gets reserved, because your potential loss is larger than the premium you received. The broker holds collateral against that risk.
How much it holds depends entirely on whether the risk is defined. A defined-risk position (a spread) caps the loss, so the collateral is just the width of the spread minus the credit. An undefined-risk position (a naked option) has a much larger — sometimes theoretically unlimited — loss, so the reserve is far bigger.
Cash-secured, defined-risk and naked
A cash-secured put reserves the full strike × 100 in cash, because if assigned you must buy the shares. A 30-strike put ties up $3,000 even though you only collected a small premium — no leverage, no margin call, the safest way to sell a put.
On a margin account, a vertical spread only reserves the max loss (e.g. a 5-wide put spread for a $1.50 credit reserves $350). A naked put instead uses a Reg-T formula — roughly 20% of the underlying minus the out-of-the-money amount, plus the premium — which can be several times the premium and rises if the stock moves against you.
Why it matters for sizing
Buying power, not the premium, is the real cost of a trade. Two trades that both collect $100 can tie up $350 and $4,000 respectively — and the return on capital is wildly different. Always judge an income trade by its credit relative to the buying power it consumes.
A margin call happens when losses push your account below the maintenance requirement. Keeping a healthy buffer of unused buying power — never deploying it all — is what lets you hold or adjust a position instead of being liquidated at the worst time.
- The premium is your income; buying power is the capital actually tied up — judge trades by both.
- Defined-risk spreads reserve only the max loss; naked options reserve a much larger Reg-T amount.
- A cash-secured put ties up the full strike in cash and can never trigger a margin call.
- Always keep a buffer of unused buying power so a move against you doesn’t force liquidation.
Frequently asked questions
Why does selling one put tie up so much buying power?
Because your risk is far larger than the premium. A cash-secured put reserves the full strike × 100 (you may have to buy the shares); a naked put on margin reserves a Reg-T amount (~20% of the underlying adjusted for moneyness). The premium is small relative to that potential obligation.
What is the difference between cash-secured and margin for a put?
Cash-secured reserves 100% of the strike in cash — no leverage, no margin call. On margin the broker reserves a smaller Reg-T amount, freeing capital but adding the risk of a margin call if the trade moves against you.
How do I avoid a margin call?
Size positions by their buying-power reduction, not the premium, and keep a buffer of unused buying power. Defined-risk spreads cap the reserve and the loss, which makes margin calls far less likely than with naked options.
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