At the Autumn Budget 2024, the government announced that the main rates of CGT applying to disposals of assets other than residential property and carried interest would increase with effect from 30 October 2024. The main rate increased from 10% to 18% for basic rate taxpayers, and from 20% to 24% for higher rate taxpayers.

HMRC says that the self assessment tax return will not automatically calculate CGT liabilities at the increased main rates and that an adjustment may be required.

HMRC’s calculator may be used where the person:

• disposed of an asset on or after 30 October 2024;
• is completing a self assessment tax return as an individual, trustee or personal representative; and
• has capital gains for 2024/25 in excess of their annual exempt amount. This is:
• £3,000 for individuals, personal representatives and trustees for disabled people; and
• a maximum of £1,500 for other trustees (or a minimum of £300 if there are any related settlements).

To use the calculator, the person must input the following information where relevant:

• the dates on which the assets were sold. HMRC’s guidance warns that anti-forestalling rules apply to counteract arrangements designed to reduce or avoid the impact of the increase in the main rates of CGT;
• the amount of the gains;
• their taxable income for 2024/25;
• details of any capital losses, noting that relief is restricted for a loss arising on a transaction with a connected person; and
• details of any contributions made to pension schemes or donations made under Gift Aid.

The calculator will then provide the adjustment amount, if any. The amount should be entered in the 2024/25 tax return in:

• box 51 of the SA108 form, if filing the return on paper; or
• the adjustment to CGT box, if filing online.

In February 2025, HMRC announced that, due to issues caused by the changes to the main rates of CGT, it would not be accepting some in-year trust and estate tax returns.