Capital Loss Harvesting: How to Use Capital Losses to Reduce Your CGT Bill 2026/27

Capital loss harvesting is a systematic approach to reducing Capital Gains Tax by deliberately crystallising losses on investments that have fallen in value, using those losses to offset taxable gains. In 2026/27, with the Annual Exempt Amount reduced to just £3,000, proactive loss management has become more important than ever for UK investors.

Why Capital Loss Harvesting Matters in 2026/27

The Annual Exempt Amount has been slashed from £12,300 in 2022/23 to £3,000 in 2026/27. At the same time, CGT rates were raised in the October 2024 Autumn Budget: investors now pay 18% (basic rate band) or 24% (higher rate) on gains from shares and investment property, with 24% also applying to residential property gains for higher-rate taxpayers.

With a smaller exemption and higher rates, gains that would previously have been tax-free now generate meaningful CGT bills. Systematically harvesting losses is one of the most effective legal methods to reduce this liability.

How Capital Losses Work

The Basic Mechanics

Capital losses arise when you sell an asset for less than you paid for it (the acquisition cost, including allowable costs such as broker fees and Stamp Duty on purchase).

Net taxable gain = Gross gains - Allowable losses - Annual Exempt Amount (£3,000)

Losses in the current tax year must be applied against gains in the same year first. You cannot choose to save current-year losses for a future year if you have gains available now. However, once current-year gains are reduced to the level of the AEA, you can stop applying losses and preserve the remainder for future years.

Carrying Losses Forward

Unused losses are carried forward indefinitely. There is no time limit on using them -- a loss realised in 2026/27 can reduce a gain in 2040/41 if you never had sufficient gains in the intervening years.

However, HMRC will not automatically know about your carried-forward losses unless you report them. You must:

• File a Self Assessment tax return for the year the loss arose, even if you would not otherwise be required to file
• Alternatively, write to HMRC to report the loss within four years of 31 January following the tax year end (so losses from 2026/27, ending April 2027, must be reported by 31 January 2032)

The 30-Day Bed-and-Breakfasting Rule

The most important constraint on capital loss harvesting is the 30-day share matching rule. HMRC introduced this to prevent investors from selling and immediately repurchasing the same shares purely to crystallise a loss.

How the Rule Works

When you dispose of shares, HMRC matches the disposal to acquisitions in this order:

1. Shares acquired on the same day as the disposal
2. Shares acquired in the 30 days following the disposal (FIFO basis)
3. Shares held in the Section 104 pool (the average cost pool of all shares in the same company)

If you sell 1,000 shares at a loss on 1 June 2026 and repurchase 1,000 shares of the same company on 20 June 2026 (within 30 days), the disposal is matched to the new acquisition on 20 June, not to your original holding. The loss is effectively neutralised.

Avoiding the Rule

There are several legitimate approaches:

Wait 30 days: Sell the shares at a loss, wait more than 30 calendar days, then repurchase. The market may move against you in the interim, but the loss will be properly crystallised.

Buy a similar but different asset: Sell a FTSE 100 tracker ETF at a loss and immediately repurchase a different FTSE 100 tracker from a different provider. The 30-day rule applies to the same shares, not substantially identical shares (though for very similar ETFs, HMRC's position is not entirely settled).

Use an ISA: The 30-day rule does not apply to purchases inside an ISA. This is the basis of the Bed-and-ISA strategy, which is discussed below.

Bed-and-ISA: Permanently Shelter Future Gains

Bed-and-ISA is the most powerful tool for managing CGT on existing holdings. The strategy:

1. Sell shares (or other investments) held outside an ISA
2. Immediately repurchase the same shares inside a Stocks and Shares ISA

Because the reacquisition is inside an ISA, the 30-day rule does not prevent the loss from being crystallised (or the gain from being realised). More importantly, all future gains and income on the ISA holding are permanently sheltered from tax.

Annual ISA Allowance Constraint

The constraint is your annual ISA subscription limit of £20,000. Each tax year you can only move £20,000 worth of investments into an ISA. Over time, a couple can move £40,000 per year into combined ISAs, building a substantial tax-sheltered portfolio.

When to Use Bed-and-ISA for Gains

Even if you are crystallising a gain (not a loss), Bed-and-ISA can make sense:

• If the gain is within or close to your Annual Exempt Amount (£3,000), you pay little or no CGT now
• Once inside the ISA, future growth is tax-free
• The ISA also removes the investment from future Income Tax on dividends (dividend allowance is only £500 in 2026/27)

Bed-and-SIPP: Reduce Gains and Get Tax Relief

Bed-and-SIPP follows the same principle as Bed-and-ISA but uses a pension (Self-Invested Personal Pension). You sell the investment outside the SIPP, crystallising the gain (or loss), then contribute cash to the SIPP and repurchase inside.

The key advantage over Bed-and-ISA is the pension tax relief. A Basic Rate taxpayer contributing £8,000 to a SIPP receives £2,000 in tax relief top-up from HMRC, effectively reducing the cost of the investment by 20%. Higher Rate taxpayers can also claim additional relief through Self Assessment.

The constraints are:

• The Annual Allowance caps pension contributions at £60,000 per year (or £3,600 if you have no relevant earnings)
• Pension funds are inaccessible until age 57 (rising to 57 from 2028)
• The Money Purchase Annual Allowance of £10,000 applies if you have already flexibly accessed pension funds

Spousal CGT Planning

Married couples and civil partners have two Annual Exempt Amounts (2 x £3,000 = £6,000 combined) and can transfer assets between them at no gain/no loss for CGT purposes.

Practical Approach

If you hold investments with accumulated gains and your spouse has spare AEA or is a Basic Rate taxpayer:

1. Transfer part of the holding to your spouse (CGT-free)
2. Your spouse then sells their portion, using their own £3,000 AEA
3. Gains in the basic rate band are taxed at 18% rather than 24%

The spouse inherits your original acquisition cost, so they will realise the same gain on disposal. But doubling the AEA and potentially halving the rate is a significant saving.

Reporting Capital Losses: The HMRC Process

You must report capital gains and losses in certain circumstances:

• Self Assessment: Required if total gains (before losses) exceed the AEA (£3,000), if you sold assets worth more than four times the AEA (£12,000), or if you need to register a loss for carry-forward
• Real Time Transaction Reporting (RTTR): The property reporting service for UK residential property disposals requires a return within 60 days of completion regardless of gain or loss
• CGT on UK Property account: Non-residents selling UK property must also report

30-Day Property Reporting

Since April 2020, gains on UK residential property must be reported and tax paid within 60 days of completion (formerly 30 days before extension). If you also make losses on other assets in the same tax year, these reduce the property gain for annual Self Assessment purposes, but you must still pay an estimate through the 60-day report and reconcile on your full return.

Loss Relief on EIS and SEIS Shares

Enterprise Investment Scheme (EIS) and Seed Enterprise Investment Scheme (SEIS) investments carry an additional loss relief not available on ordinary shares. If an EIS or SEIS investment fails, the loss (reduced by the Income Tax relief already received) can be offset against income rather than only capital gains.

For a Higher Rate taxpayer, an EIS loss of £10,000 on shares where 30% Income Tax relief of £3,000 was received:

• Effective loss: £7,000
• Set against income at 40%: tax saving of £2,800

This makes EIS and SEIS loss relief particularly valuable as a downside mitigation tool.

Common Capital Loss Harvesting Mistakes

Forgetting to report losses. If you do not file a return or write to HMRC within four years, your losses expire. Even if you did not owe any tax, report the losses to preserve them.

Triggering the 30-day rule accidentally. If you sell and repurchase within 30 days, not only is the loss neutralised, but you also have an unexpected gain treatment on the second disposal using the new acquisition cost.

Offsetting losses against gains in the wrong order. Current-year losses must be used against current-year gains before AEA. Carried-forward losses are only used to the extent gains exceed the AEA.

Not considering transaction costs. Selling and rebuying incurs bid-offer spread and broker commissions. If the expected tax saving is small relative to transaction costs, the trade may not be worthwhile.

The Bottom Line

Capital loss harvesting is straightforward in principle but requires careful attention to timing (the 30-day rule), reporting obligations (file within four years to preserve losses) and sequencing (current losses before AEA, then carried-forward losses). With the AEA at just £3,000 and CGT rates at 18%/24% in 2026/27, even modest gains can generate meaningful tax bills. Combining loss harvesting with Bed-and-ISA transfers and spousal planning creates a comprehensive CGT management strategy that can save thousands of pounds over time.