The government increased the main rates for capital gains tax (CGT) in the budget on 30 October 2024 to 18% and 24%.
A mid-year change like this can lead to people underreporting and underpaying any tax they owe.
HMRC adjustment calculator
To help with this change, HMRC have developed an online calculator which will work out an adjustment to include on your return so that the correct amount of tax is declared and paid.
Example
Joan has income of £52,000 and made a gain of £8,000 when she sold her ABC plc shares on 1 November 2024.
After deducting her annual CGT allowance of £3,000, her chargeable gain is £5,000.
Joan is a higher rate taxpayer, so CGT is due at 24% on the £5,000 chargeable gain.
However, HMRC systems will charge the ‘old’ rate of 20% in the tax return calculations.
The calculator will give an ‘adjustment’ of £200 for Joan. This is the difference between the tax due on the 24% and 20% tax rates and what would otherwise be underreported and underpaid without further action.
Using the calculator
You’ll need to use the calculator if you have total gains in excess of your annual tax free exemption for the year (relating to your Dodl general investment account, or a different provider), and some of those gains were made on or after 30 October 2024.
To use it, you’ll need:
· The date you sold or transferred (disposed) of the investment(s)
· The amount of gain
· Your taxable income for 2024/25
· Details of any losses
· The amount you paid into pensions (gross)
· Details of any charity donations that qualify for gift aid (gross)
Any disposals you’ve made in your Dodl general investment account will be shown in your annual tax summary in date order. You can find this by logging into your account and selecting the bell ‘🔔' icon and general investment account in the ‘your documents’ menu.
If you have gains both before and after the tax rates changed on 30 October 2024, the HMRC calculator will set your annual exempt amount against gains arising at the new (increased) rates of CGT first.
If you’re completing an online return for the 2024/25 tax year, this must be filed, and any tax paid by 31 January 2026. Paper returns are due by 31 October 2025.
If you pay the wrong amount of tax and still owe money after 30 days, a 5% fine applies, with an extra 5% after six and 12 months. You’ll also be charged interest on late payments. The rate will be base rate plus 4% from the due date until the payment date.