Track up to 90 days spent in the UK during the current UK tax year. Spending 90 days does not by itself determine your UK tax residence status. Under the Statutory Residence Test, your residence status may also depend on your UK ties and other automatic residence tests. The UK tax year runs from 6 April to 5 April.
https://www.gov.uk/government/publications/rdr3-statutory-residence-test-srt/guidance-note-for-statutory-residence-test-srt-rdr3
UK Tax Residency — 90 Days
90 days in the UK in the current tax year