Iron butterflies and pinning

An iron butterfly is a short straddle with a long strangle around it: sell the at-the-money call and put, buy a further-out call and put as wings. It is the credit version of the long butterfly, with the same payoff, and it is the natural bridge between the condors of Module 3 and the butterflies of this one. This lesson prices it, compares it with a condor, and then covers pinning, the expiration-day behavior that butterfly traders talk about and often misunderstand.

The iron butterfly

XYZ at $50, 45 days, IV 30%.

• Max profit: the credit, $335, at a pin on $50.
• Max loss: wing width − credit = $5.00 − $3.35 = $1.65, $165, below $45 or above $55.
• Breakevens: $50 ± $3.35 = $46.65 and $53.35.
• Buying power: one wing width minus the credit, $165.

Line for line, the long call butterfly from the previous lesson, and the Greeks match it too, as parity says they must. The iron version uses out-of-the-money wings on both sides, which usually means tighter markets and easier fills, and it arrives as a credit, which changes nothing about the risk.

Iron butterfly versus iron condor

Both are two credit verticals. The condor's short strikes are apart; the butterfly's are the same strike.

The butterfly risks a third as much to collect four times more, and gets paid at all half as often, with the full payment only at a pin. Same expectancy, different shape. The condor suits "I think it stays in a range"; the butterfly suits "I think it goes nowhere" or "I have a specific target."

Because the full profit requires the pin, iron butterfly management differs from condor management:

• Take profit at 25% of the credit (buy back at about $2.50) rather than 50%. Waiting for 50% means waiting for the last two weeks.
• A 1× credit stop does not exist: the max loss is only half the credit. Use a stop of half the max loss (about $80) or the 21-day rule, whichever comes first.
• Directional versions move the center strike above or below the price; a $52 iron butterfly on a $50 stock is a mildly bullish trade with a lower credit.

Pinning

"Pinning" is the tendency of a stock to close on or very near a strike price with large open interest on expiration day. The mechanism is dealer hedging. Market makers who are net long options near that strike are long gamma: as the stock rises above the strike they sell shares to stay neutral, as it falls below they buy. That hedging flow pushes the price back toward the strike from both sides, and the effect is strongest in the last hours when gamma is largest. Academic studies have found the effect is real and small: a few percent more closes near strikes than chance would predict, mostly in large, heavily optioned names.

Two things follow for a butterfly trader:

1. Do not plan on it. A small statistical tendency is not a reason to hold a butterfly into the close hoping for the last $2 of the tent. The gamma of the two short center options at that point is enormous; a late-day move of $1 costs more than the pin would have paid.
2. Know the risk that shares its name. Pin risk is what happens when the stock closes within pennies of your short strike. With XYZ at $50.02 at the bell, the short $50 call is $0.02 in the money and may or may not be exercised by its holder; you learn on Saturday whether you are short 100 shares over the weekend. With the stock at $49.98 it is the put. The only way to avoid finding out is to close the short center options before the bell, even if it means giving up a few cents.

Expiration day: value of the short $50 straddle vs. price, last hour

  Straddle
   2.00 |  \                    /
   1.00 |   \                  /
   0.50 |    \                /
   0.00 |     \______________/  <- the "pin": worth nothing here,
        +----+----+----+----+      worth $1 per $1 away, in either
        48   49   50   51   52     direction, within minutes

Key idea: An iron butterfly sells the ATM straddle and buys wings: same payoff as the long butterfly, delivered as a credit with buying power equal to wing width minus credit. It collects far more than a condor for a third of the max loss and pays in full only at a pin, so take profit at 25% and never hold the center strike into the last hour. Pinning is real, small, and not a plan; pin risk is the reason to close before the bell.

Try it: Build the 45/50/55 iron butterfly and the 39/44 – 56/61 iron condor side by side in the options profit calculator. Record credit, max loss, breakevens, theta and vega for each. Then set the date to 21 days out with the stock at $50 and record each position's value as a percentage of its credit. Note which one is closer to its profit target.

Recap

• Iron butterfly: sell the ATM call and put, buy OTM wings; credit is the max profit at a pin, wing width minus credit is the max loss.
• 45/50/55 on a $50 stock: credit $3.35, max loss $1.65, breakevens $46.65 and $53.35.
• Versus a condor: four times the credit, a third of the max loss, half the probability of any profit; same expectancy, different shape.
• Manage at 25% of credit or half the max loss; do not wait for the pin.
• Pinning is a small dealer-hedging tendency; pin risk is the unknown assignment on a strike closed within pennies. Close the center before the bell.