Selling RSU, ESPP, SAYE or SIP shares: what is my CGT cost?

By Jason Bull, a part-time trader who writes about UK capital gains tax for people doing their own returns. 2 October 202610 min readCGT guides

For most employee shares, your capital gains cost is what you paid plus the amount charged to income tax when you got them. So an RSU costs its value on the day it vested, and a SAYE share usually costs just the price you paid. SIP shares are the exception: they cost their market value when they leave the plan.

After that they are ordinary shares. They join one pool with shares of the same class that you bought yourself outside an ISA. The same-day and 30-day rules apply to them as to any other shares.

The four schemes side by side

Scheme	Income tax	Your CGT cost	Source
RSU	On the market value at vest, usually through payroll	The value taxed at vest	ERSM20194; ERSM140095; HS287
ESPP, from a US parent	On the discount, when you buy	Usually the market value on the purchase date	CG56337; HS287
SAYE	None when you buy, normally	The option price you paid	HS287; CG56450
SIP	None after 5 years in the plan	The market value on the day they leave the plan	HS287; ITEPA 2003 s505

Source: HMRC helpsheet HS287 (2026), sections 3, 4, 9 and 11; ERSM20194; ERSM140095; CG56337; CG56450; ITEPA 2003 s505.

RSUs: the vest value is your cost

An RSU is a promise of shares. No shares are delivered until the award vests. HMRC tax the vest under the rules for securities options. In HMRC's own example the employee is charged "on the market value of the shares received at vesting". Your employer usually collects the tax through PAYE.

That taxed amount then counts as part of what you paid for the shares, so the same value is not taxed twice. HS287 sets your cost as anything you paid plus "the amount chargeable to Income Tax on the exercise". You are treated as acquiring the shares "at the date when you exercise your option". For an RSU we read that as the vest date.

If the shares are priced in dollars, your payslip shows the amount taxed in pounds. Since HS287 makes the taxed amount the cost, we read that sterling figure as your cost. A later sale is converted at the date you sell, as our guide to HMRC exchange rates explains.

Shares sold to pay the tax

Many plans sell some shares on the vest day to pay the tax. HMRC call this "sell to cover", and you still acquired every share. HMRC's guidance says "the full entitlement of securities has been beneficially acquired by the employee", even when a broker sells them for you. So the sale is a disposal.

It is matched with shares you acquired on the same day, which are the ones that vested. They cost their vest value and sold at about that price, so the gain is nil or close to it. A dealing fee or a small move in the price leaves a small gain or loss. If you file a return, the proceeds still count towards the £50,000 of sales that brings in the capital gains pages.

Other plans keep some shares back and pay the tax in cash. HMRC call this net settlement, and in their example "the employee only receives net shares". In our reading the shares kept back were never yours, so there is no sale of them to report. On the same reading, each share you do receive still costs its full vest value.

A worked example: 100 RSUs vest at £50

On 15 June 2026, 100 of your RSUs vest when the shares are worth £50. You are taxed on £5,000 as pay. Your plan sells 47 of them that day at £50 to cover the tax, for £2,350.

The same-day rule matches those 47 with 47 of the shares that vested. Their cost is 47 × £50, which is £2,350. So the gain is nil. The other 53 go into your pool at £2,650, or £50 each.

On 10 March 2027 you sell the 53 at £70, for £3,710. Take off their £2,650 cost and the gain is £1,060. That is inside the £3,000 tax-free allowance, so with no other gains there is no tax to pay.

The 47 sold on the vest day are matched with shares that vested that day, so only the later sale of the 53 makes a gain.

Shares you bought yourself share the pool

Your pool holds every share of the class "acquired by the same person in the same capacity", however you got it. Say you already held 97 of the shares in a dealing account, bought over the years for £3,350. The 53 vested shares join them, and each share in the pool now has "the same average cost": £40.

Date	What happens	Shares	Pool cost (£)	Average (£)
Before 15 June 2026	Shares you bought	97	3,350.00	34.54
15 June 2026	53 vested shares join	150	6,000.00	40.00
10 March 2027	You sell 53	97	3,880.00	40.00

Source: TCGA 1992 s104(1); HS284 (2026).

The sale of 53 now takes 53 × £40 of cost, which is £2,120. The gain is £3,710 less £2,120, which is £1,590 rather than £1,060. You cannot pick the RSU shares to sell. Pooled shares are "indistinguishable parts of a single asset", and the matching rules decide which ones you sold.

Shares that vest in the 30 days after a sale are matched with it before the pool is. A vest on 8 April 2027 would be matched with your 10 March sale, at its own vest value. That holds even though it falls in the next tax year.

ESPP shares from a US plan

A US parent's employee stock purchase plan is usually outside the UK's tax-advantaged schemes. So the discount is taxed as income. If your employer does not take that tax through payroll, you report it on a Self Assessment return.

Your cost is usually the market value on the purchase date. Say you pay £85 for a share worth £100, and £15 is taxed as income. If the plan gives you an option, your cost is what you paid plus the amount taxed: £85 plus £15. If it is a discounted purchase, your cost is the market value. Either way it is £100.

Some plans stop you selling for a while. Until that restriction ends, the shares are a different class and stay out of your pool. HS287 sets out their cost.

SAYE: the option price, and 90 days for an ISA

Under SAYE you save for 3 or 5 years, then can buy shares at a price fixed at the start. You do not pay income tax or National Insurance on the difference between that price and what the shares are worth. So your cost is "usually what you pay for them when you exercise your option".

That price can be as low as 80% of the market value when the option was granted, and the shares may have risen since. Buy at £4 when they are worth £9 and each share already carries £5 of gain.

You can move the shares into a stocks and shares ISA and pay no CGT, "on the transfer or on the later disposal". You have 90 days from exercising, and the shares count towards your £20,000 ISA limit. The window is for SAYE and SIP shares only.

It moves shares, not cash. A MoneySavingExpert forum member asked on 29 August 2025 whether "the money from the sale of the shares" could go into the ISA. HS287 describes a transfer "directly from" the scheme. Sell first and you have made a disposal, which paying the cash into an ISA does not undo. That is a bed and ISA.

SIP: the 3-year and 5-year points

SIP shares are a separate class from your other shares while they stay in the plan. Sell them from inside the plan and you have no CGT to pay. Keep them in for 5 years and you pay no income tax or National Insurance on their value.

Take free or matching shares out within 3 years and income tax is usually charged on their market value when they leave. From 3 to 5 years, it is on the lower of their value when awarded and when they leave. For partnership shares, the lower figure compares the salary you used to buy them with their value when they leave.

Shares leaving the plan are treated for CGT as sold and bought back at market value, with no gain on that step. So your cost is "their market value on the date the shares leave the plan", whatever income tax was due. Keep them and they join your pool at that value. Or move them into an ISA within 90 days of leaving the plan.

Before you sell, list every batch you received with its date and number of shares. Beside each, write what you paid and the amount taxed. Take them from the plan's confirmation and your payslip.

To work one vest through, TaxBull's RSU and ESPP tax calculator shows the income tax and National Insurance on it, what the shares you kept cost, and the tax when you sell them.

TaxBull's capital gains tax calculator for shares reads Morgan Stanley StockPlan's Releases and Withdrawals reports. Each vest enters your pool at its vest-date price, converted at HMRC's monthly rate. Where fewer shares were delivered than vested, only those go in and no sale is recorded. So count any sell-to-cover proceeds towards the £50,000 yourself, with any small gain or loss on them. For another plan, enter each batch as a buy in the generic CSV. TaxBull pools by the symbol in each file, so give the plan's shares the ticker your broker uses for the same class of share. A Releases report with no Symbol column uses the plan name instead, such as "GSU Class C". To use your payslip's sterling figure, type an exchange rate on that row.

Sources

This is general information, not tax advice. The figures here are for 2026/27. Check gov.uk or ask a tax professional about the year you are filing.

Work out your own capital gains tax from your broker exports.

All posts