Options and UK Capital Gains Tax: How CGT Works on Options Trading

The one fact that decides almost everything: an option is its own asset for Capital Gains Tax. It is not part of the shares it points at. A call you bought, and the stock it lets you buy, are two separate things in HMRC's eyes — taxed on two separate timelines.

This guide covers exchange-traded equity options held by a private investor — the ordinary case, where gains fall under CGT. Only if your activity amounts to a trade (the badges of trade) does it become income tax instead, which is rare for individuals. Every number below is real output from our calculator, not a hypothetical.

When you buy an option

You pay a premium up front. From there, exactly one of four things happens, and each has its own tax outcome.

• It expires worthless. For a traded option, the expiry is a disposal for nil proceeds, so the whole premium is an allowable loss in the tax year it expires.
• You sell it before expiry. Normal disposal. Gain or loss is the sale price minus the premium you paid.
• You exercise a call. No gain or loss on the option itself. The premium is added to the cost of the shares you buy, and stays there until you sell them.
• You exercise a put. The premium becomes an incidental cost of selling the shares — it comes off your proceeds.

One trap on the first point: the allowable loss applies to traded options. For a private, non-traded option (a bespoke contract that isn't exchange-listed), HMRC's general rule gives the holder no loss relief on a lapse — see the worked examples in CG12350 and CG12351. Nearly all retail options are exchange-traded, so the loss is usually allowable — but it's worth knowing the line.

What a disposal looks like in a report

Here's a long call run end to end. You buy one AAPL $150 call for $5.00 a share and later close it for $12.00, paying $1 of fees each way. Because it's a USD contract, each leg is converted to sterling at HMRC's rate for the month it falls in. Taking an example rate of $1 = £0.80:

The fees fold into each leg automatically — the $501 cost is $500 of premium plus the $1 fee, and the $1,199 proceeds are $1,200 less the closing fee. The currency point matters more than it looks: if the closing trade had landed in a month where the rate was £0.78 rather than £0.80, the gain would come out at £534.42, not £558.40. The calculator pulls the right HMRC monthly rate for each leg, so a move in the exchange rate between opening and closing becomes part of your gain.

Exercise and assignment reach into your shares

This is the part people miss. When an option is exercised, it doesn't produce a gain of its own — instead it rewrites the cost or proceeds of the share trade it triggers. Exercise a call and the premium is added to what the shares cost you. Get assigned on a put you wrote and the premium comes off what the shares cost you.

Here's a cash-secured put taken all the way through assignment, again in USD across three different monthly rates:

You collected $299 of premium in January, were assigned in February and had to buy 100 shares, then sold them in April. The premium you took for writing the put reduces your cost basis in those shares — £11,317.80 becomes £11,078.60 — so when you sell, the chargeable gain is £1,213.20. The option and the shares are settled as one joined-up transaction, exactly as CG12351 describes.

Writing options: taxed now, sometimes unwound later

Writing — selling an option to open — has a timing quirk that catches people out. Granting an option is itself a disposal under section 144 TCGA 1992, so the premium you receive is a chargeable gain straight away, in the tax year you write it. There's no matching cost, so the whole premium is taxable.

If it lapses, that gain stands and you're done. If it's exercised, the grant is unwound, merged with the share trade, and the tax on the premium is set off or repaid — which can mean amending the year you wrote it, if exercise falls in a later year.

Our Interactive Brokers example report has a lapse case in it. A call written for a $250 premium that expired worthless:

The $250 premium converts to £192.13 at the month's HMRC rate, there's no cost against it, and the whole £192.13 is the gain — declared in the year the option was written, just as HMRC's grantor example sets out.

Every option is a separate asset

This is where options part company with shares. Shares of the same class go into one Section 104 pool and share an average cost. Options don't blend like that. An option is defined by its underlying, its type, its strike, and its expiry — change any one and it's a different asset.

A £50 call and a £55 call are two assets. A call and a put are two assets. June and September expiries are two assets. So a single multi-leg strategy — an iron condor, say — is four separate disposals, not one position you net off at the end. Each leg is calculated on its own.

Why this gets hard by hand

None of the individual rules is complicated. The trouble is volume and bookkeeping. A handful of spreads turns into dozens of separate assets, each with its own outcome — some reaching back to change the cost of shares or rewrite a prior year's return, all of it in dollars that need converting at the right monthly rate. Brokers hand you fills, not disposals.

Our CGT Calculator treats each option as its own asset, applies the right outcome for expiry, sale, exercise, and assignment, folds exercised premiums into the matching share trades, and converts every leg at HMRC's monthly rate — across 60+ strategies. Upload your broker export and the disposals fall out the other side.

Sources and further reading

• Section 144 TCGA 1992 — options: grant, exercise, and abandonment
• HMRC CG12300 — Capital Gains Manual: options, introduction
• HMRC CG12350 — worked example: call option (grant, exercise, abandonment)
• HMRC CG12351 — worked example: put option
• HMRC CG55536 — traded options: tax treatment summary
• HMRC exchange rates — the monthly rates used to convert USD legs to sterling
• Live IBKR example report — option disposals calculated end to end