Capital Losses Explained

How allowable capital losses offset gains, when unused losses carry forward, and share matching rules to watch.

Reviewed against official HMRC guidance

Tax year
2026/27
Last reviewed
August 2026
Reading time
5 min

How capital losses help

Who this guide is for: For investors who have disposed of assets at a loss and need to understand same-year offsets, carry-forward and share matching traps.

An allowable capital loss arises when you dispose of an asset for less than its allowable cost (subject to the Capital Gains Tax rules).

Losses reduce chargeable gains in the same tax year. Unused amounts can usually be carried forward. For the overall Capital Gains Tax workflow, see Capital Gains Tax Explained.

Same-year versus carried forward

  1. Step 1Same-year losses against gains
  2. Step 2Brought-forward losses if needed
  3. Step 3Annual Exempt Amount
  4. Step 4Tax any gain left
Illustrative ordering — confirm HMRC rules on GOV.UK.
Illustrative ordering — confirm HMRC rules and the Annual Exempt Amount on GOV.UK.
StepWhat happens
1Offset current-year allowable losses against current-year gains (per HMRC ordering)
2Apply brought-forward losses if gains remain
3Apply the Annual Exempt Amount to remaining gains
4Tax any gain still left at the relevant Capital Gains Tax rates

Share matching traps

Buying back the same shares within 30 days can change which acquisition is matched to the sale. That may defer or restrict the loss you expected.

See how capital losses affect your taxable gain Use the Capital Gains Tax Calculator

Frequently asked questions

Can I choose which gains to offset first?

Allowable losses are set against gains in line with HMRC's ordering rules. You generally cannot ignore a gain just to preserve losses without following those rules.

What if losses exceed gains this year?

Unused allowable losses can usually be carried forward to later tax years. Keep claims and computations so you can use them later.

What is the 30-day share matching rule?

If you sell shares and buy the same class back within 30 days, special matching rules can restrict loss claims (sometimes called bed-and-breakfasting rules). Check GOV.UK before crystallising losses.

Do I need to report a loss?

You should claim allowable losses to carry them forward. Deadlines apply — see GOV.UK capital losses guidance.

Official sources

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Next steps

This guide is for general information only. It is not tax, legal or financial advice. Always check the official guidance for your situation.