The deadline for submitting your 2020-21 Self-Assessment tax returns online is 31 January 2022. You should also be aware that payment of any tax due should also be made by this date. This includes the payment of any balance of Self-Assessment liability for the 2020-21 plus the first payment on account due for the current 2021-22 tax year.
https://www.gov.uk/government/news/self-assessment-deadline-countdown-begins
