Miscalculation - Tax calculation

Hi, If I made 10k gbp 8 years ago but did not file self assessment then as I had thought it was offset against sufficient losses (now realising I made losses in different tax year), and now realising this now, how much is the penalty fees that would be charged against me? How do I calculate this? This would be my first time ever filing a self assessment as I had always thought I was in -ve/losses. Thanks

The above is in reference to stocks and shares gain.

Hi,
Please follow the guidance at:
Calculate interest and penalties for tax years ending 5 April 2004 to 5 April 2023
You disclose the tax using the world wide disclosure facility at:
Make a disclosure using the Worldwide Disclosure Facility
Thank you