Assignment, dividends and expiry risk

From an exercise notice to shares in the account

An option writer never chooses the moment of assignment. The holder decides whether and when to exercise; the clearing house then picks a writer. What the writer receives, and how fast it must be paid for, depends on the contract.

Early exercise is only possible on American-style options. For a UK reader that means ICE UK stock options (the 1,000-share standard contracts and the 100-share minis that ICE lists on 22 large names, where a broker has to confirm that it offers them and quotes a two-way price) and US equity and ETF options. The FTSE 100 index options on ICE, the Mini FTSE 100 dailies, and SPX and XSP in the US are European: they can be exercised only at expiry, and they settle in cash, so no shares ever arrive. The OIC notes that most, but not all, US index options are European, so the contract specification is the place to check.

On an American contract the chain from exercise to assignment has five steps. At ICE Clear Europe, equity-option exercises are allocated at random, one lot at a time, so every short lot in the series has the same chance of being picked; allocations are made separately for each clearing member's own account and each of its customer accounts (ICE Clear Europe Clearing Procedures, section 5.8). OCC in the US also assigns at random to clearing members. A US broker then passes the assignment to one of its customers by a fixed method, first-in first-out or random, which FINRA must approve and which the broker must explain to customers in writing (FINRA Rule 2360(b)(23)(C)). A UK broker's method for its own customers is set out in its terms, not in ICE's procedures.

Two consequences follow. First, the writer's position changes on the exercise date, not on the morning the notice arrives, and the tax computation uses that date too (TCGA 1992 s28(2): where a contract is conditional on the exercise of an option, the disposal and acquisition happen when the condition is met). Second, the cash or shares are due on the settlement date: for an ICE assignment on a Thursday, the Monday after. UK markets plan to move to one-day settlement (T+1) from 11 October 2027; the latest step recorded on the FCA's page (updated 13 August 2026) is the draft regulations the Government published on 20 November 2025, and we could not find an ICE statement on how settlement of its stock options will change (checked 27 September 2026).

Expiry Friday, hour by hour in UK time

Three expiry processes run on the same Friday and a UK reader sees all three, because the London and US sessions overlap only in the afternoon. The diagram shows a normal week, such as Friday 16 October 2026, and a mismatch week, such as Friday 19 March 2027, when the US has moved its clocks and the UK has not.

The US hours move with daylight saving. US clocks change on the second Sunday of March and the first Sunday of November; UK clocks on the last Sundays of March and October. In the weeks between, the US session is 13:30 to 20:00 UK and the 17:30 Eastern cut-off is 21:30 UK. The March 2027 monthly expiry, Friday 19 March, falls inside one of those weeks. The canonical table of US hours and cut-offs is on the US options page.

Who pays the 0.5% stamp tax when shares change hands

Stamp duty reserve tax (SDRT) is charged at 0.5% when a physically settled option over UK shares is exercised, on the consideration for the shares, which is the strike price (HMRC STSM113030). The person liable is the purchaser of the shares (Finance Act 1986 s91). Writing an option is not chargeable (STSM113010). So the tax follows whoever ends up buying:

On a 100-share mini the charge is a tenth of that: a Tesco mini put assigned at 450p costs £2.25. There is no UK SDRT on US shares delivered by a US option (GOV.UK: stamp duty or SDRT is not normally due on foreign shares bought outside the UK), and none on cash-settled FTSE 100 options, because no shares change hands.

The rule changes what an income strategy on a UK share really costs. In a wheel on a UK name, the 0.5% arises on the put-assignment leg and on any share purchase, not when the shares are later called away: a Tesco 450 put assigned on a standard contract costs £22.50 in SDRT, while the call-away at the end of the cycle costs the writer nothing. On a covered call the exercising holder pays, which is one reason the holder's early-exercise arithmetic below includes it. Interactive Brokers passes the stamp duty on an exercise through to the client and also charges its option commission on UK exercises and assignments (£1.40 a contract on its tiered rate, £1.70 fixed; checked 26 September 2026).

Two refinements. Recognised options intermediaries can claim relief from the charge on hedge purchases and on purchases made by exercising listed options (STSM112120), and ICE confirmed in Circular 25/123 that the reliefs apply to deliveries under its single-stock options. That relief is why a market maker's exercise arithmetic differs from a private holder's. Separately, buying an existing physically settled option over UK shares is in principle within SDRT (STSM113020; GOV.UK lists "an option to buy shares" among the purchases taxed). ICE options are opened and closed against the clearing house, and we could not confirm SDRT being collected on ordinary ICE option trades (checked 27 September 2026): the 0.5% that readers meet in practice is the one on delivery of the shares.

BP's 12 November ex-date: which calls are worth exercising the evening before

A call holder who wants a dividend has to own the shares before the ex-dividend date. The London Stock Exchange's dividend timetable puts the record date on a Friday and the ex-date one business day earlier, so that a purchase with standard two-day settlement made the day before the ex-date is on the register on the record date. BP's third-quarter ex-date is Thursday 12 November 2026 (bp financial calendar). An ICE exercise lodged by 18:30 on Wednesday 11 November is a purchase at the strike on Wednesday, settling on Friday 13 November, the record date. The writer picked for assignment is told on Thursday morning, when the shares are already trading without the dividend.

The holder compares two numbers on Wednesday evening. Exercising is worth the intrinsic value, 530p minus the strike, and captures the dividend. Not exercising leaves a call on a share that opens about one dividend lower on Thursday: its value is the European value with the dividend taken out of the share price. The table prices both with the site's pricing model for the November calls, with BP still at the 530p model level on Wednesday 11 November, nine days to the Friday 20 November expiry, and the 6.39p dividend assumed (Model inputs, below). A gain from exercising for the holder is the same amount lost, compared with not being assigned, by the writer who is picked; the 0.5% SDRT is paid only by a holder without intermediary relief.

Three groups appear. The 480 and 500 calls are worth exercising for anyone: even after SDRT the holder is £34.31 or £21.38 a contract better off, so a writer of those calls can treat assignment on Wednesday night as the expected outcome. The 510 call is the grey zone: an intermediary with SDRT relief gains £27.37, while a private holder paying £25.50 in SDRT gains £1.87, or 47p after the £1.40 exercise commission. Because the holders who exercise include intermediaries with the relief described above, a writer cannot count on the private holder's column. From 520 up, holding is worth more than exercising: at the ex-dividend price of about 523.6p the 520 call is barely in the money and keeps more time value than the dividend is worth.

For the writer of a covered 500 call, assignment on Wednesday night means delivering 1,000 shares at 500p on Friday, keeping the original premium, and losing the £63.90 dividend. Compared with holding shares and short call through Thursday unassigned, that is £46.38 worse. Buying the call back on Wednesday does not avoid it: the market prices an American call at about its exercise value by then (the model's American value is 30.05p against 30.00p intrinsic), so the buy-back costs about the same as being assigned. The decision point is earlier, whenever a short call is deep in the money with an ex-date before expiry. The tax of the assignment is one computation: the premium is added to the sale proceeds of the shares, dated Wednesday 11 November 2026, in 2026/27 (written options).

Brokers act on the same arithmetic. Interactive Brokers says that where a client holds a call spread before an ex-date and it expects the short call to be assigned while the account could not meet the dividend liability or margin, it may exercise the long calls or close the spread itself, and that the client could lose money if it exercises and the short call is not then assigned.

Deep in-the-money puts: the interest on the strike

Puts are exercised early for a different reason. A put holder who exercises receives the strike now instead of at expiry, and gives up whatever protection the put still has. With interest at 3.75% (Bank Rate, held on 17 September 2026), 530p received 30 days early earns 1.63p a share. When the put is so deep in the money that the rest of its value is worth less than that interest, exercising wins. Dividends push the other way: a share falls by the dividend on the ex-date, which adds to a put's intrinsic value, so put holders tend to wait until the ex-date has passed. Early put assignment is therefore most likely after an ex-date and when the put is far below the strike, the reverse of the call case.

The chart shows the gap between the two thresholds. The European value dips below intrinsic from about 478.8p, where the interest on the strike first exceeds the value of the same-strike call. The American put is worth exercising only below about 460.3p, because a holder who waits also keeps the right to exercise later, which is worth something until the put is deeper still. The threshold rises as expiry approaches and there is less interest left to earn:

Worked assignment. A writer sells one BP October 530 put on Monday 17 August for 20.75p, £207.50 a contract (model value 20.86p, filled on the 0.25p tick). Suppose BP has fallen to 460p by Thursday 8 October, eight days before expiry. The American value is exactly the 70p intrinsic (the European value is 69.57p), so a holder gains by exercising that evening. If the writer is picked:

• The purchase of 1,000 BP at 530p is dated Thursday 8 October; the notice arrives on Friday.
• On Monday 12 October the account pays £5,300.00 for the shares, £26.50 SDRT and a £1.40 assignment commission: £5,327.90.
• For capital gains tax the premium reduces the cost of the shares (TCGA 1992 s144(2)(b)). The commissions and the stamp tax are incidental costs (s38(2)). Base cost: £5,300.00 + £26.50 + £1.40 + £1.40 − £207.50 = £5,121.80, acquired on 8 October 2026.
• At 460p the shares are worth £4,600.00, so the position stands at −£521.80 after the premium and every cost. That is £27.90 worse than if the put were still open at its 70p intrinsic value (the SDRT and the assignment commission), and £5,327.90 of cash is now committed instead of the put's margin.

A later dividend changes the timing. The November 620 put, with BP at 530p on Wednesday 11 November and the 6.39p ex-date the next day, is worth 96.32p against 90p intrinsic: the holder waits, because the share is about to fall by the dividend. On Thursday, with BP at 523.61p after the drop, the same put is worth exactly its 96.39p intrinsic and is worth exercising.

One leg of a spread assigned: the BP October 520/480 put spread

A credit put spread is usually described by its maximum loss. The example: on Monday 17 August a writer sells the BP October 520 put for 16.25p and buys the 480 put for 4.50p (model values 16.21p and 4.46p, filled on the 0.25p tick; 60 days, IV 26% for both strikes, American pricing). The net credit is 11.75p, £117.50 a contract. The spread is 40p wide, £400, so at expiry the most it can lose is £400.00 − £117.50 + two £1.40 commissions = £285.30, and the most it can make is £114.70. Under strategy-based margin the broker holds about that maximum loss (spread margin).

Now take the same path as above: BP at 460p on Thursday 8 October. The short 520 put is worth exactly its 60p intrinsic, so it is a candidate for exercise that evening, while the long 480 put, 20p in the money, is worth 20.99p. If the short leg is assigned, the writer wakes on Friday holding 1,000 BP bought at 520p, owing £5,200.00 + £26.00 SDRT + £1.40 commission = £5,227.40 on Monday 12 October, and still holding the 480 put. The spread has become shares plus a protective put. Three ways out, priced on Friday with BP still at 460p and the put at a model value of 20.78p, 20.75p on the tick (seven days left):

Both closing routes lose more than the £285.30 "maximum": the exercise route by £28.80, which is the £26.00 SDRT plus the assignment and exercise commissions, and the sale route by £21.30, because the put's remaining value takes some of that back. The defined-risk formula leaves out the stamp tax a put writer pays when assigned on a UK share. The larger change is in capital: the account's requirement jumps from roughly the maximum loss to the full cost of 1,000 shares overnight, and if the account cannot carry that the broker can close positions itself. With only seven days left the long put's time value is small, so exercising it gives up only £7.50 against a sale on the tick; with weeks left, selling it would usually be worth more than exercising, which is the OIC's general point about exercise versus sale. The rolling page covers closing or rolling a spread before this point.

Why "defined risk" is only defined at expiry

The maximum-loss figures on the spread and condor pages (the formulas are on the Level 2 page) assume both legs end on the same day at the same price. With American, physically settled legs on ICE or US exchanges that assumption can fail in three ways:

1. Early assignment of the short leg, as in the section above: the economics stay close to the formula if the long leg is used, but the cash and margin do not.
2. An expiry close between the strikes. The short leg is in the money and is exercised automatically; the long leg is out of the money and lapses. The account then holds a share position with no option attached over a weekend.
3. A close at or near the short strike (pin risk, next section), where the writer cannot know until the notices arrive whether shares will appear.

Worked case: a close between the strikes. The BP 520/480 put spread reaches Friday 16 October with BP closing at 500p. Settled as options, the result would be £117.50 − £200.00 − £2.80 = −£85.30. In practice the 520 put, 20p in the money, is exercised against the writer and the 480 put expires. On Tuesday 20 October the writer pays for 1,000 BP at 520p plus £26.00 SDRT. If BP opens on Monday 19 October at 450p after weekend news, the result from entry stands at £117.50 − £700.00 (70p below the 520p cost on 1,000 shares) − £2.80 − £1.40 − £26.00 = −£612.70 at Monday's open: £327.40 beyond the −£285.30 "maximum loss". Nothing on the chain was wrong; the long 480 put had simply expired on Friday, so it could not protect against a fall on Monday.

The same structure on a European, cash-settled contract has no such gap. A FTSE 100 put spread on ICE settles both legs in cash on one number, the EDSP, on one day, so its loss at expiry is the formula's figure and nothing is left open afterwards. A FTSE 100 vertical is therefore the cleanest example of risk that really is defined. On American stock options a spread's risk is defined if both legs are closed, or both are exercised or abandoned together, before the deadlines; the brokers' own expiry procedures (below) show what happens otherwise.

Pin risk, and automatic exercise at ICE and OCC

Pin risk is uncertainty, not a loss in itself: when the share closes at or very near a short strike on expiry day, the writer cannot know whether the option will be exercised, so cannot know whether a share position will exist on Monday. It matters most when the position is large relative to the account, and when the share can move before the exercise deadline.

At ICE. Once the exercise deadline has passed on expiry day, ICE's systems exercise every option that meets the automatic-exercise settings in its contract terms; members who do not want an option exercised can send an abandon instruction before the deadline where the terms allow it (ICE Clear Europe Clearing Procedures, section 5.5). The procedures give one tick in the money as the setting for several contracts, but do not state the setting for UK equity options, so the working rule is the broker's own. Saxo, for example, exercises every in-the-money long option and assigns every in-the-money short at expiry, does not support abandoning an in-the-money position, and describes one tick in the money as the typical convention. For BP, one tick is 0.25p: a settlement price of 519.75p leaves a short 520 put in the money and likely to be assigned, while 520.25p leaves it out of the money. Between the 16:30 last trade and the 18:30 deadline a holder can still decide, so a close that sits on the strike leaves the outcome open until the notices arrive.

At OCC. US options use exercise by exception: an expiring equity or index option in the money by $0.01 or more is exercised unless the clearing member instructs otherwise (OCC Rule 805(d), as explained by the OIC). A holder can override it in either direction with a contrary exercise advice: not exercising an option that would be exercised, or exercising one that would not (FINRA Information Notice, 17 November 2025). The decision can be made until 17:30 Eastern, 22:30 UK, while the shares are still trading after hours. For a UK writer that means a US position's fate is settled late in the evening on news the writer may not see; the next section works an example.

A short call assigned without the shares

A call writer who does not own the shares and is assigned ends up short the shares. It happens on an uncovered call, when the short leg of a call spread is assigned and the long call is not exercised, and on a covered call where the shares have been sold or moved to another account. The shares must be delivered on the settlement date, so the broker borrows them for the account (at a fee) or buys them in. While the short position is open over an ex-date, the account owes the lender an amount equal to the dividend: on BP's assumed November dividend, 6.39p a share, £63.90 a contract. In the US the OIC puts it plainly: a call holder who exercises before the ex-date is entitled to the dividend, and the assigned writer, covered or not, must deliver the shares plus the dividend.

Worked example, in dollars and pounds. A UK reader is short the $100 call in a $100/$105 call spread on a US share, expiring Friday 16 October 2026. The share closes at $99.95 at 21:00 UK, so both calls are out of the money and would lapse. At 21:40 UK the company publishes news and the share trades at $101.50 after hours. Before the 22:30 UK cut-off, a holder of the $100 call sends a contrary exercise advice and exercises it. The $105 call lapses. The writer's account is short 100 shares at $100 from the exercise date, settling on Monday (T+1). If the share opens on Monday at $102.00, buying back 100 shares costs $200 more than the $100 received: £147.50 at an illustrative $1.356 per £1 on 17 August 2026 (the premium received first offsets part of it). A gap to $103.00 would cost $300, £221.26. Had the share opened above $105, the lapsed $105 call could no longer have capped the loss: the spread's defined risk ended with Friday's expiry. There is no UK SDRT on US shares.

Two account rules follow from this. Short selling needs a margin account, which is why a cash account can write calls only against shares it holds, and puts only against cash it holds, both restricted while the option is open (Interactive Brokers: covered calls with the stock "available and ... then restricted"; see account types and permissions). And an uncovered call needs a margin account with the broker's highest option permission, where margin rises as the share rises (uncovered margin).

What brokers do in expiry week

Clearing-house rules set the outer deadlines; each broker's terms decide what happens inside them. Two published policies show the range (checked 27 September 2026):

An instruction not to exercise an in-the-money long option is the tool for a holder who could not pay for the shares. On US contracts it is the contrary exercise advice described above; at ICE it is an abandon instruction, available where the contract terms and the broker allow it. Saxo's terms do not allow it for in-the-money positions, so for a Saxo client who cannot fund the shares the remaining route is to sell the option before the close. The broker comparison page lists each broker's option access and fees (feature matrix).

Adjusted contracts after a corporate action

A standard ICE contract "normally" covers 1,000 shares. ICE's product pages add that corporate-action adjustments can leave some series with a non-standard contract size, and ICE publishes a list of them. A share split, rights issue, special distribution, merger or demerger can therefore turn a contract into one that delivers a different number of shares, or a basket of shares and cash. Saxo describes the two usual adjustment methods, a ratio change and a package of deliverables, follows the exchange's notice, and reserves the right to close positions before the ex-date where it cannot support the adjusted deliverable, particularly after spin-offs and demergers. Before exercising or being assigned on an adjusted series, the contract's deliverable is the number to check: the strike times 1,000 is no longer the cash that changes hands.

What assignment does to the capital gains computation

Exercise and assignment fold the option into the share transaction; there is no separate option gain or loss to report. The date is the exercise date (TCGA 1992 s28), even though the shares settle later.

Cash-settled FTSE 100 options follow a different rule: for the writer, grant and settlement become one transaction at settlement, which can produce a loss (s144A(2)); for the holder, the cash received is the proceeds of disposing of the right to it (s144A(3)). Shares acquired on assignment also count for the 30-day matching rule if the same shares were sold in the previous 30 days. The canonical worked examples, with the SA108 boxes, are on the UK options tax worked examples page (see also the 30-day rule with options); options cannot be held in an ISA at all (wrappers).

An expiry-week review, in numbers

Most of the surprises on this page come down to a handful of numbers that can be written down before expiry week. For the BP 520/480 put spread above they are:

Self-check before the Level 1 structures

The Level 1 page's cash-secured put and covered call both end in assignment when they go wrong, or sometimes when they go right. These questions use this page's own numbers; the working is in each answer. Nothing is scored.

Where these mechanics decide the outcome

These strategy pages apply this page's rules to their own positions: covered call (ex-date assignment), cash-secured put (put assignment and SDRT), wheel (both legs), collar (the short call against held shares), bull put spread (one leg assigned), iron condor (a close between strikes), poor man's covered call (short call assigned without shares) and uncovered short call.