Short Straddle
Prerequisite strategies: you must have traded the iron butterfly and the short strangle to a written plan, plus the cash-secured put and covered call beneath them. Clear the Level 3 gate first.
Why this structure exists
Every short-premium structure is paid for accepting a range. The iron condor buys wings that cap the bill. The short strangle removes the wings and widens the range. The short straddle removes the range as well: both legs sit on the money, so the position collects the largest credit available in the expiry — and is guaranteed to finish with one leg in the money, because the index does not settle on a round number.
That changes what you are betting on. A strangle bets the index stays inside a band; a straddle bets on the size of the move, whichever way it goes — you win if the distance travelled by expiry is less than the credit. It is the purest way to be short implied volatility, and its P&L is dominated by one number: gamma.
Here is the concentration, in figures from the worked example. Set the 9,000 straddle beside the strangle a reader of the tier below would sell on the same expiry — short the 8,500 put and the 9,550 call, the nearest listed strikes to the 16-delta convention, deltas −0.145 and +0.154. The straddle carries 1.71× the strangle's gamma (−£1.57 against −£0.92 of delta per 100 index points), and it carries that gamma at the price the index is trading at now, not 500 points away. Its breakeven band is ±0.79 standard deviations against the strangle's −1.14 to +1.24 — modelled, a 57.2% chance of any profit against 76.6%. The straddle is not a strangle with the risk turned up. It is a lower-probability, higher-credit trade that cannot be held, only managed.
Why not just sell the strangle instead? Because that strangle collects £782.02, so it takes 5.13 contracts to match the straddle's £4,015 credit — and 5.13 contracts consume £46,211 of buying power against the straddle's £13,500, then lose £62,755 in the same 20% gap to 7,200 that costs the straddle £13,993. Concentration buys capital efficiency and a smaller tail, and pays for it with 19 points of win rate. If you want the win rate, sell the strangle in smaller size. If you cannot manage a position daily, sell neither.
Construction
| Leg | Buy / Sell | Quantity | Strike rule | Expiry rule | Target delta | Price |
|---|---|---|---|---|---|---|
| Call | SELL (credit) | 1 contract = £10 per index point | Nearest strike to spot | 30–60 DTE; never a weekly | +0.51 | 203.5 pts = £2,035.30 |
| Put | SELL (credit) | 1 contract, same strike, same expiry | Same strike as the call | Same expiry | −0.48 | 198.0 pts = £1,980.07 |
| NET | Net credit | 1 straddle | 9,000 strike, 9,000 spot | 45 days | −0.03 (−£0.31/pt) | 401.5 pts = £4,015.37 |
Three hard inequalities, checked on the chain before the order goes in:
Formulas: max profit = (credit − round-trip costs) × multiplier, and only if settlement is exactly at the strike. Breakevens = strike ± net credit in points. Loss at settlement = (|settlement − strike| − net credit) × multiplier, with no upper bound on either side.
The dashed line is the position; the solid line is the payoff, and they only meet at the edges. At the strike the gap between them is the entire £4,007 credit — a short straddle is worth almost nothing until the last few days, while carrying the whole of the gamma throughout. The dashed curve assumes a flat 16% implied volatility; in a real fall volatility rises and pushes its left half lower still.
Entry criteria
| Gate | Rule | Reason |
|---|---|---|
| IV rank / percentile | IVR ≥ 50 and IV percentile ≥ 50 | You are short £250.86 of vega per volatility point; entering cheap is the single commonest way to lose |
| Term structure | Front month in backwardation to the second month | An inverted curve is the market pricing an event; a flat or contango curve means you are selling the cheap end |
| Skew | 25-delta put IV minus 25-delta call IV within its own 12-month range | Steep skew means the downside is already bid; the ATM put you sell is the cheapest part of a frightened chain |
| Days to expiry | 30–60, closed at 21 | Gamma at 7 DTE is 2.55× gamma at 45 DTE. You want the theta, not the last three weeks |
| Strike | Nearest listed strike to spot; modelled delta +0.51 / −0.48 | Off-the-money is a strangle wearing a straddle's name |
| Liquidity | Spread ≤ 3% of the straddle mid; open interest ≥ 250 both legs | You must be able to close in a panic. ICE UK single-stock series routinely fail this |
| Event calendar | No MPC decision, US CPI, index review or quarterly future roll inside the window | The straddle is short exactly the thing an event delivers |
Do not enter if: IV rank is below 50; initial margin exceeds 5% of net liquidation value; you already hold short premium in a correlated underlying (in a volatility event they are one trade, not two); you cannot watch the position intraday; or you cannot state, in pounds, the margin requirement after a 20% gap.
Greeks at entry and how they evolve
| Greek | Entry, 45 DTE, 9,000 | 22 DTE, unchanged | 7 DTE, unchanged | +1 SD (9,506, IV 14%) | −1 SD (8,494, IV 20%) |
|---|---|---|---|---|---|
| Delta (£ per point) | −0.31 | −0.22 | −0.12 | −7.46 | +5.62 |
| Gamma (£/pt per 100 pts) | −1.57 | −2.25 | −4.00 | −0.88 | −0.98 |
| Theta (£ per day) | +44.20 | +63.67 | +113.40 | +21.66 | +37.50 |
| Vega (£ per vol point) | −250.86 | −175.86 | −99.37 | −137.03 | −174.88 |
Black–Scholes, 16% implied volatility unless stated, 4% rates, 3.5% index dividend yield, per one £10-a-point contract.
Gamma decides this trade, and the table shows why the time stop is not a preference. Holding from 45 DTE to 7 DTE multiplies theta by 2.6 and gamma by 2.55: the income and the danger rise together, and the income is visible daily while the danger arrives once. The position's character flips the moment the index leaves the strike — at entry net delta is −£0.31 a point, effectively flat; one standard deviation up it is −£7.46 a point, the same exposure as being short roughly £70,900 of FTSE 100. You did not choose that short. Gamma chose it, and it will keep choosing.
FTSE 100 at 9,000, implied volatility 16%, 45 days to run
The ICE FTSE 100 index option is worth £10 per index point (£90,000 at 9,000), is European style so it cannot be exercised early, settles in cash against the Exchange Delivery Settlement Price, ticks in 0.5 points (£5), trades 08:00–16:50 London, and on the third Friday stops trading as soon as reasonably practicable after 10:15. All prices below are modelled, not live quotes.
The trade: sell 1 × FTSE 100 9,000 call and 1 × FTSE 100 9,000 put, same expiry.
Branch A — the target fires. Implied volatility falls and the straddle marks 301.2 points.
Branch B — tested. FTSE 8,600 with 30 days left, IV up to 21%.
Branch C — the gap. FTSE opens 7,200, down 20%, IV 45%, 45 days left.
Branch D — held to settlement at an EDSP of 9,120. The put expires worthless, the call settles for cash at 120 points. Profit = £4,015.37 − £1,200.00 − £4.00 = £2,811.37. Nothing is delivered, no stamp duty arises, and no assignment notice appears.
On an ICE UK single stock instead the trade is a different animal. A BP 530 straddle at 45 days and 26% implied volatility collects only about 38.4p × 1,000 shares = £383.82; the series are physically delivered and American style; and because one leg is always in the money at expiry, assignment is close to certain — either you buy 1,000 shares for £5,300 and pay £26.50 of SDRT, or you deliver 1,000 you may not own. Add a bid-ask that can exceed 10% of the straddle on a thin chain and the structure fails its own liquidity gate. That is the teaching point: the short straddle is a UK index trade or it is not a UK trade.
This is a single, hand-picked, favourable scenario. It is not a typical or expected outcome. Every premium here is modelled from Black–Scholes at the stated inputs, not taken from a live chain, and the 9,000 index level is an illustrative round number rather than a quote. Real fills are worse. Past performance, including any illustrative example shown here, is not a reliable indicator of future results.
Management and adjustment
| Trigger | Diagnosis | Action | Do NOT do this |
|---|---|---|---|
| Net delta beyond ±£2.00 a point | Gamma has turned a neutral trade directional | Roll the untested strike toward the money for a net credit | Roll the tested strike away — that is buying back your loss at the worst price |
| Tested strike breached, credit still > inversion width × £10 | Defensible: an inverted strangle still has a profit zone | Invert. Here: 8,600 call / 9,000 put, total credit £5,397.49 against a £4,000 inversion | Invert without doing the arithmetic. If credit ≤ width × £10 the inverted position cannot profit at any settlement |
| Loss reaches 100% of credit (£4,015.37) | The trade has failed on its own terms | CLOSE. Both legs, one order | Roll for a net debit, add contracts, or "give it time" — short gamma does not mean-revert on request |
| Implied volatility expands after entry | Vega loss, −£250.86 a point at entry | Hold if delta is inside the band and the stop is intact; higher IV also makes any roll richer | Panic-close a vega loss that has not yet become a delta loss |
| Implied volatility collapses after entry | The thesis paid, early | Take the 25% target the day it appears, whatever the DTE | Hold for the remaining theta. You are collecting £44 a day against £1.57 of gamma |
| Underlying gaps through a strike | Undefendable | Close at the open. Size the loss, not the hope | Anything else. Every adjustment at a gap adds risk to a position already too big |
| 21 days to expiry reached | Gamma is about to double | Close, or roll the whole straddle out to the next monthly for a credit | Carry it into expiry week to "collect the last bit" |
| Margin usage > 50% of net liquidation value | The broker is now managing the position, not you | CLOSE enough contracts to get back under 25% | Wait for the margin call. Forced liquidation happens at the worst prices of the day |
ROLL WHEN the index is still inside the band, the untested side can be moved toward the money for a net credit, and more than 21 days remain. ROLL TO the same expiry (a strike roll) or the next monthly (a duration roll), never both in one order — you will not know which decision worked. DO NOT ROLL a credit position for a net debit, ever: that is the mechanism behind almost every blown short-premium account. And the case nobody writes down: when the loss reaches the credit, or when defending would take buying-power usage above half of net liquidation value, the correct action is to close, not to adjust. Defence has a budget. Past it, "adjustment" is a bigger position with a better story.
Exit rules
If all four are silent, do nothing and check net delta again tomorrow. Here, "nothing" is an active decision costing £1.57 of gamma a point.
Margin and broker reality
A cash account cannot hold this and neither can a standard margin account without uncovered-option permission. In practice you also want portfolio margin, and Interactive Brokers UK requires USD 110,000 of net liquidation value to upgrade an existing account, and restricts margin-increasing trades once the account falls below USD 100,000. That number, not confidence, is the gate for most UK retail.
The figures below use the published strategy-based schedule that IBKR's own options margin page sets out for an uncovered broad-based index option, and which matches the Cboe strategy-based rule it derives from — chosen here because you can recompute it yourself: 100% of the option's market value, plus the greater of 15% of the index value less any out-of-the-money amount, or 10% of the index value; and for a straddle, the greater of the two legs' requirements plus the market value of the other leg. Maintenance uses current market value where initial uses entry proceeds — which is why the requirement rises automatically as the options you sold get more expensive. Note that IBKR margins the ICE FTSE 100 series itself on a risk-based model rather than this schedule, so the number in your own order preview governs; the direction of travel does not change, and neither does the mechanism.
Liquidity is a margin-equivalent cost. The ICE FTSE 100 chain is the only UK-underlying options market deep enough for this structure; ICE UK single-stock series are not, and a 10% spread on a £383.82 straddle is a £38 tax on entry and again on exit.
Stress test
| Scenario (move at once, 45 DTE left) | Index | Mark-to-market P&L | P&L if held to expiry | Maintenance margin |
|---|---|---|---|---|
| −2 SD, IV 26% | 7,988.8 | −£6,705.08 | −£6,104.99 | £22,699.60 |
| −1 SD, IV 20% | 8,494.4 | −£2,399.29 | −£1,048.81 | £19,152.23 |
| Unchanged, IV 16% | 9,000.0 | −£4.00 | +£4,007.37 | £17,515.37 |
| +1 SD, IV 14% | 9,505.6 | −£1,669.81 | −£1,048.81 | £19,939.61 |
| +2 SD, IV 13% | 10,011.2 | −£6,140.21 | −£6,104.99 | £25,168.44 |
| −20% gap, IV 45% | 7,200.0 | −£14,765.43 | −£13,992.63 | £29,576.79 |
One standard deviation over 45 days at 16% implied volatility is 505.6 points. Implied volatility is stepped up on down moves and down on up moves to reflect equity index skew; that asymmetry is why −1 SD costs £729 more than +1 SD on the marks.
Read the last column before the third. In every adverse row the requirement rises while the equity falls — the mechanism by which short-premium accounts are closed by their broker rather than by their trader. On 19 October 1987 the FTSE 100 fell 10.8% and then a further 12.2% the next day, 21.7% across two sessions; on 12 March 2020 it fell 10.9% in one. A 20% overnight gap is not the tail of this distribution, it is the part of it that has already happened. Size for the row you have not modelled: if a −20% gap across your whole short-premium book would cost more than 10% of net liquidation value, the book is too big — and the independence you assumed between "unrelated" short-premium positions disappears on exactly the day you need it.
every roll must be executed for a net credit AND total credit collected > inversion width × multiplier. If either fails, you do not have an adjustment. You have a loss, and the only question is what size you take it at.What to trade instead
Simpler, from the tier below: the iron butterfly is this trade with wings bought. It gives up part of the credit and caps the loss at a number you can write down, removing the margin spiral, the liquidation threshold and most of the reason this page needs a stress test. For nearly every UK retail account it is the correct expression of the same view, and the £13,500 of buying power this straddle consumes will fund several of them.
Alongside, at the same tier: the short strangle trades credit for probability — 76.6% against 57.2% modelled, but at 5.13 contracts and 3.4 times the buying power for the same money. Take the straddle only for the capital efficiency, and only if you can manage daily.
More precise, at this tier: the big lizard is a short straddle with the upside obligation bought back by a call spread — the only version of this structure where "no risk to the upside" can be proved arithmetically before entry.
Risk statement
Uncovered options are among the highest-risk instruments available to a retail client: losses are not limited to the amount invested, can exceed the account balance, and the broker may liquidate positions without notice. This is educational material about mechanics, margin and UK tax treatment, not a recommendation to trade the FTSE 100 or anything else, and it takes no account of your circumstances. Every figure here is modelled rather than quoted. If your trading is frequent enough to raise the investor-versus-trader question, that is one for a qualified adviser.