Iron butterfly

An iron butterfly (often called an "iron fly") is a short straddle with insurance. You:

• Sell an at-the-money call and an at-the-money put at the same strike: a short straddle.
• Buy an out-of-the-money call above that strike and an out-of-the-money put below it, usually the same distance away.

All four options share one expiry. The short straddle brings in a large credit; the bought "wings" cost part of it but cap the loss if the price moves far. It is one of the most common ways Indian index option sellers turn the open-ended risk of a short straddle into a defined one. The straddle guide explains the core position.

How the payoff works

• At the middle strike at expiry: all four options expire worthless and you keep the whole credit. This is the peak of the payoff.
• Moving away from the middle: one sold option gains intrinsic value. Profit falls point for point and turns into a loss past the breakeven.
• Beyond either wing: the bought option offsets further losses. The loss is fixed at its maximum.

The payoff looks like a tent: a sharp peak at the middle strike, sloping sides, and flat floors on both sides. Compare that with the flat top of an iron condor.

Max profit = net credit · Max loss = wing width − net credit · Breakevens = middle strike ± net credit

A worked NIFTY example

NIFTY is at 25,000. You expect a quiet session or week around this level. You place four orders:

The short straddle alone collects ₹310; the wings cost ₹95, leaving ₹215. Wing width = 300. Maximum loss = 300 − 215 = ₹85. Breakevens = 25,000 ± 215 = 24,785 and 25,215.

Here the possible profit (₹215) is larger than the possible loss (₹85), the reverse of an iron condor. The catch: the price must finish very close to 25,000 for a large profit, and the profitable zone is only 430 points wide. With a lot of 75 units (check the current lot size on NSE or with your broker), that is up to ₹16,125 of profit against up to ₹6,375 of loss.

Live example: the straddle at the centre of the fly

The credit in an iron butterfly comes mostly from the at-the-money straddle. Here is today's NIFTY straddle, minute by minute, with its VWAP:

A falling straddle line is good for an iron fly seller: the core position is losing value. A rising line means movement or fear is picking up, which hurts. Many intraday sellers treat the straddle crossing above its VWAP as a warning sign, as covered in the intraday short straddle guide.

The option chain shows what the wings cost at each distance:

Start at the at-the-money row: its call plus put is the straddle credit. Then read the call price a few strikes up and the put price a few strikes down; their sum is what the protection costs. Nearer wings cost more and lower the maximum loss; further wings cost less and raise it.

Choosing the wing width

• Narrow wings (close to the middle): a smaller credit, a smaller maximum loss, a safer but less rewarding trade.
• Wide wings: a bigger credit, closer to a naked short straddle, with a larger maximum loss.
• A common reference: setting the wings around the expected move, so the protection starts roughly where the market thinks the move ends.

The strategy builder shows the payoff, both breakevens and the maximum loss for any wing width you try.

Iron butterfly vs iron condor

• Credit: the iron fly sells at-the-money options, so it collects much more.
• Sweet spot: the fly's maximum profit is at one point; the condor keeps full profit across a range.
• Reward to risk: the fly usually offers more reward per unit of risk; the condor offers a higher chance of some profit.
• Sensitivity: the fly reacts strongly to every move near the middle (high gamma, especially near expiry); the condor is calmer until the price nears a sold strike.

A cousin of the iron fly, the butterfly spread, has the same tent shape but is built from calls only (or puts only) and is paid for up front instead of collecting a credit.

Intraday iron flies on expiry day

Many Indian traders open an iron butterfly in the morning of an index expiry day and close it by 15:15 or earlier. Expiry day suits the trade because the at-the-money straddle loses time value fastest in its last hours. It is also when the risk is sharpest: with so little time left, a 100-point move can change the position's value very quickly (high gamma), and the profitable zone is narrow.

Those who trade it this way usually set a fixed loss limit on the whole position in rupees, decide in advance whether they will shift the body if NIFTY moves, and avoid opening it just before scheduled news. Check your broker's margin rules for expiry day, since some brokers change them on the last day of a contract.

Managing an iron butterfly

Because the profit peak is so narrow, few iron flies are held for the full credit. Common practice:

• Take a partial profit, for example a quarter to a half of the credit, once time decay has done its work.
• Exit at a set loss, often in rupees on the combined position, or when NIFTY reaches a breakeven.
• Shift the body: if the price moves a lot, close the fly and open a new one centred on the new at-the-money strike. This resets the trade but locks in the loss so far.

The same ideas apply to a short straddle; the adjustment guide covers them in depth. Time decay is the profit engine here, and it is fastest close to expiry, as the theta guide shows.

Common mistakes

• Expecting the maximum profit. It needs the price to end exactly at the middle strike.
• Removing the wings to collect more. That returns to an unlimited-risk short straddle.
• Holding through events where a gap can jump straight to the maximum loss.
• Adjusting too often. Each shift costs four sets of charges and slippage.
• Running stock iron flies to expiry, which can lead to physical delivery.