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Credit Spreads: Executable Credit, Defined Expiration Risk, and Assignment Control

Analyze bull put and bear call credit spreads with signed executable cash, fees, quantity and deliverable matching, valid break-evens, closing debits, assignment, margin, and cash-settlement controls.

Updated

For educational purposes only; not investment advice. Investing may result in loss.

Direct answer

A standard credit spread is a matched vertical that sells one option and buys a farther-out option of the same type, underlying claim, expiration, exercise style, settlement method, multiplier, deliverable, and quantity. A bull put spread sells the higher-strike put and buys the lower-strike put; a bear call spread sells the lower-strike call and buys the higher-strike call.

The opening credit is cash received against an open obligation, not earned profit. Expiration loss is defined only while the exact long leg remains valid and matched. Fees, executable closing prices, early or partial assignment, adjusted deliverables, quantity mismatch, margin liquidation, and settlement operations can make the account path differ from the clean expiration diagram.

A signed, executable spread ledger

Let Q be spread units, M the compatible multiplier, K_s the short strike, K_l the long strike, B_s the executable opening bid for the short, A_l the executable opening ask for the long, and F_entry all opening fees. Define net opening cash N_entry = Q × M × (B_s − A_l) − F_entry and net credit per underlying unit C_net = N_entry / (Q × M). For a standard bull put, K_s > K_l; for a standard bear call, K_s < K_l; in either case width is W = |K_s − K_l|.

  1. Lock each leg’s root, option type, side, strike, expiration, style, settlement, currency, multiplier, live deliverable, and quantity. A familiar ticker or 100 multiplier does not prove compatible adjusted claims.
  2. Build the entry ledger from synchronized executable B_s and A_l, visible size, actual complex-order fill, and F_entry. Midpoints, model marks, last trades, or a credit label without its sign convention do not establish cash received.
  3. For a matched bull put at expiration, calculate Π_put(S_T) = N_entry − Q × M × max(K_s − S_T, 0) + Q × M × max(K_l − S_T, 0). For a matched bear call, calculate Π_call(S_T) = N_entry − Q × M × max(S_T − K_s, 0) + Q × M × max(S_T − K_l, 0).
  4. Only when 0 ≤ C_net ≤ W and the legs remain matched is maximum gain N_entry, expiration maximum-loss amount Q × M × W − N_entry, bull put break-even K_s − C_net, and bear call break-even K_s + C_net. A negative credit or credit above width is a control exception, not a standard conclusion.
  5. Before expiration, value both legs with synchronized executable sides. If closing the short costs A_s and selling the long receives B_l, all-in close cash outflow is C_close = Q × M × (A_s − B_l) + F_close, and realized option P/L is N_entry − C_close; it is not the change in a midpoint mark.
  6. Map exercise and settlement separately. American short legs can be assigned early or partially; the broker does not necessarily exercise or sell the long automatically. European cash-settled legs use their contract’s official settlement value and create cash debits or credits rather than shares.
  7. Reconcile fills, ratio, remaining contracts, shares, strike cash, official settlement, fees, margin, corporate adjustments, tax lots, and broker records. Close or exercise the long only after confirming the short obligation and any remaining extrinsic value.

Worked examples

  • Executable bull put entry and close. Sell Q = 2 puts at K_s = $100.00 for B_s = $1.85 and buy two puts at K_l = $95.00 for A_l = $0.70, with M = 100 and four opening contracts charged $0.65 each. Then F_entry = $2.60, N_entry = $227.40, C_net = $1.1370, maximum gain is $227.40, expiration maximum-loss amount is $1,000 − $227.40 = $772.60, and break-even is $100.00 − $1.1370 = $98.8630. At S_T = $97.00, P/L is $227.40 − $600 = −$372.60; at S_T = $94.00, the long puts offset $200 of the $1,200 short-put debit and P/L is −$772.60. If the short ask is later $2.60, the long bid $1.10, and closing fees $2.60, then C_close = ($2.60 − $1.10) × 200 + $2.60 = $302.60 and realized P/L is $227.40 − $302.60 = −$75.20.
  • Executable bear call expiration. Sell one call at K_s = $100.00 for $2.20, buy one call at K_l = $105.00 for $0.85, use M = 100, and pay F_entry = $1.30. Net opening cash is N_entry = $133.70, so C_net = $1.3370, break-even is $101.3370, maximum gain is $133.70, and expiration maximum-loss amount is $500 − $133.70 = $366.30. At S_T = $103.00, P/L is $133.70 − $300 = −$166.30; at S_T = $107.00, the long call offsets gains above $105.00 and P/L remains −$366.30.
  • Assignment and the long leg’s extrinsic value are separate. In a one-unit physical bull put with short K_s = $100.00 and long K_l = $95.00, suppose stock is $92.00 and the short put is assigned early. The account pays $10,000 and receives 100 shares. The long put has an executable bid of $3.20: selling it receives $320, so event cash is −$10,000 + $320 = −$9,680 while the shares are worth $9,200, an event mark of −$480 before the original spread cash and fees. Exercising the long put instead sells the shares for $9,500, an event result of −$500; selling preserves $20 of executable extrinsic value. Assignment timing is not chosen, and the original spread ledger remains separate.
  • A quantity mismatch removes the loss cap; cash settlement changes the ledger. Sell two K_s = $100.00 puts but buy only one K_l = $95.00 put, all with M = 100, and receive N_entry = $300. At S_T = $0.00, P/L is $300 − $20,000 + $9,500 = −$10,200; below $95.00, each further $1 decline still loses $100, so this is not a defined-risk 1:1 spread. Separately, a matched cash-settled index bear call with K_s = 4000, K_l = 4050, M = $100 per point, N_entry = $1,200, and official S_settle = 4072 has settlement P/L $1,200 − $7,200 + $2,200 = −$3,800. It creates no shares, and an ETF or screen close cannot replace the official value.

Risks and controls

  • Similar roots, share classes, expirations, or currencies can represent different claims.
  • A reversed buy-sell side or debit-credit sign changes the strategy and cash ledger.
  • Strike order determines whether the position is a bull put or bear call credit spread.
  • Unequal quantities or multipliers leave residual naked-option exposure.
  • Corporate actions can change deliverables and destroy apparent leg compatibility.
  • Different exercise styles or settlement methods prevent ordinary vertical netting.
  • Executable short bids and long asks can be worse than displayed midpoint marks.
  • Complex-book depth may not support the desired number of spread units.
  • Separate or partial fills can create temporary or lasting uncovered exposure.
  • Commissions, exchange charges, assignment fees, and exercise fees reduce the credit and change break-even.
  • N_entry is cash against an open obligation, not realized income.
  • A closing debit must use executable short ask and long bid, not a stale mark.
  • American short options can be assigned early around dividends or financing incentives.
  • Partial assignment can create shares and leave an unmatched residual spread.
  • The long option is not automatically exercised or sold when the short is assigned.
  • Exercising a long option can forfeit executable extrinsic value.
  • Pin, after-hours moves, exercise-by-exception, contrary instructions, and broker cutoffs affect expiration inventory.
  • Cash settlement uses an official value; physical settlement can require an exact adjusted basket.
  • Regulatory or house margin, buying power, and liquidation policy can change after entry.
  • Gaps, volatility, skew, liquidity, taxes, corporate actions, and record errors can defeat the planned account result.

Common misconceptions

  • “A credit means profit.” It is opening cash paired with a short-option obligation.
  • “Maximum loss is always width minus credit.” That requires matched quantity, multiplier, deliverable, expiration, settlement, and intact legs, and excludes later costs.
  • “The long leg prevents assignment.” It limits matched expiration economics but cannot stop exercise of the short.
  • “Positive Theta guarantees income.” Net Greeks vary with spot, time, volatility surface, and the two legs’ different sensitivities.
  • “Closing or rolling erases the loss.” Closing realizes the old spread; a roll adds a new entry and new obligation.

Authoritative sources

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