A holder's outlay is fixed and paid up front; a writer's is a margin requirement that is recalculated every day. On Cboe Bitcoin U.S. ETF Index options, purchases of puts or calls with nine months or less to expiration must be paid for in full, while writers of uncovered puts or calls deposit and maintain 100 percent of the option proceeds plus 20 percent of the aggregate contract value, minus the amount by which the option is out of the money, per Cboe's CBTX contract specifications. The condition that caps the writer's requirement from below is a floor of the proceeds plus 10 percent.
The holder pays once; the writer keeps posting
Those two sentences describe the whole asymmetry. The buyer's maximum loss on the option itself is the premium, fixed at trade entry. The writer receives that premium once and carries a requirement that moves with the index level, because 20 percent of aggregate contract value is 20 percent of the current index level times $100, as the CBTX specifications define it.
Nothing about that requirement is a loss limit. It is collateral that has to be there tomorrow as well.
Four roles, and which two have the open end
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| Role | Right or obligation | Cash at entry | Ongoing requirement |
|---|---|---|---|
| Call holder | Right to buy at the strike | Pays the premium in full | None |
| Put holder | Right to sell at the strike | Pays the premium in full | None |
| Call writer | Must sell at the strike if assigned | Receives the premium | Margin, recalculated daily |
| Put writer | Must buy at the strike if assigned | Receives the premium | Margin, recalculated daily |
The holder rows end at the premium. A published payoff table makes the shape concrete: in the example in the Risk Disclosure Statement for Security Futures Contracts, a customer who buys an XYZ 50 call covering 100 shares at $5 per share pays a $500 premium, and at expiration prices of $50, $45 and $40 the result is the same $500 loss each time. The loss stops. The writer's does not.
Example: the margin behind one uncovered CBTX call
Assume the Cboe Bitcoin U.S. ETF Index at 60.00 and an uncovered 65 call written for 1.50. Those levels are assumed; the formula and the $100 multiplier are from Cboe's CBTX specifications.
Option proceeds: 1.50 x $100 = $150. Aggregate contract value: 60.00 x $100 = $6,000, and 20 percent of that is $1,200. The call is out of the money by 65 - 60.00 = 5.00 points, or $500, so the deduction is $500 and the calculation gives $1,200 - $500 + $150 = $850.
Now check the floor. The minimum for calls is the proceeds plus 10 percent of aggregate contract value: $150 + $600 = $750. Since $850 is above $750, the requirement is $850.
The buyer on the other side of that contract paid $150 and owes nothing further. The writer collected $150 and has to hold $850, recalculated as the index moves. When the collateral behind a written position runs short, the sequence that follows is in a margin call can end in liquidation.
Assignment is random, and most contracts are never exercised
Holders exercise about 7 percent of options, and OCC assigns those exercise notices to clearing member accounts using a random procedure, states OCC's options assignment FAQ. The assigned firm then allocates by an exchange-approved method, usually random or first in, first out.
Low frequency is not protection. The writer cannot know which contracts are in the 7 percent, and the allocation is not tied to who bought the contract originally.
European exercise closes the early-assignment window
Cboe's CBTX specifications set European-style exercise, meaning the contracts can generally be exercised only on the expiration date, with cash delivered the business day after. That removes early assignment from the writer's calendar; it does not reduce the margin requirement, which stays on the position until it is closed or expires.
The limits that cap either side
Position and exercise limits sit at 24,000 contracts for CBTX, and ten Cboe Mini Bitcoin U.S. ETF Index options count as one standard contract for aggregation, the same specification sheet states. Strike intervals are no less than $5.
Those limits apply to holder and writer alike. What each side owes inside them is the part that differs, and the premium being paid or collected is broken apart in what is inside an option premium.
Source references
Primary sources used for this guide. Follow the links for the original scope, definitions and conditions.
- Cboe Bitcoin U.S. ETF Index Options Contract SpecificationsAccessed 2026-09-17
- Risk Disclosure Statement for Security Futures ContractsAccessed 2026-09-17
- Options Assignment FAQAccessed 2026-09-17