Hi,
Capital gains tax is a separate tax to income tax and has its own allowance.
Your income tax liability is based on your income from interest and dividends and must be calculated first.
If you have no tax to pay after your personal allowance of £12570 is applied, you have the full range of the lower rate of capital gain to apply against your capital gain, after your annual exempt allowance (£6000 for 23/34) is deducted.
The lower rate for capital gains is 10% and the higher rate at 20%.
Please have a look at the guidance at:
Report and pay your Capital Gains Tax
Thank you.