Hi
Both countries have the right to tax the gains from the disposal of the property.
As the property is located in the USA, the double taxation treaty, will give the USA the first rights to tax the gains arising from the disposal of the property, so you will pay tax there.
HMRC can also tax the capital gain from the disposal of an overseas property.
To avoid being taxed twice on the gains, you would claim a tax credit of up to 100% of the tax paid in the USA, in the foreign sections of the self assessment tax return.
This credit will be set against the UK capital gains tax, so that you do not pay the tax twice.
SA100 (tax return) SA106 (foreign) SA108 (Capital gains) and any other supplementary pages that are appropriate.
The property is a residential property, so the gain should be shown in the section for residential property and will be taxed at the rates of 18% and 28%.
You can download the paper supplementary pages at
Self Assessment
If you submit the tax return online, you would tick yes to the foreign sections and capital gains section, as well as those other sections that are appropriate.
Thank you