You need to be careful in calculating these 180 days. It is not based on typical year from January to December. It is any consecutive 12 months. For example:
You travelled on 1st of June 2019, and came back on 27th of November 2019 (179 days).
Then, you travelled on 1st of January of 2020 to 5th of January 2020 (4 days).
In the example above, it is true that you travelled only 179 days in 2019 and 4 days in 2020. But you WONT be eligible for ilr because you travelled for more than 180 days on the period between May 2019 and April 2020 (12 consecutive months)
Another example explaining the different between the rules before and after 11 Jan 2018: Please find the whole "Indefinite leave to remain: calculating continuous period in UK" guidelines:
https://assets.publishing.service.gov.u ... gov-uk.pdf
For settlement applications made from 11 January 2018, you must consider
absences from the UK on a rolling basis, rather than in separate consecutive 12-
month periods. If the applicant’s qualifying period includes leave granted before this
date, any absences during that leave will be considered under the previous rules – in
separate 12-month periods ending on the date of application.
For example:
The application date is 30 June 2020. The applicant’s continuous period includes the
following grants of leave:
• one grant of leave from 1 July 2015 to 28 July 2018 – any absences during this
grant of leave will be considered in separate 12-month periods, ending on 30
June each year
• one grant of leave from 29 July 2018 to 30 June 2020 – any absences during
this grant of leave will be considered on a rolling basis: you must not include
any absences from the previous grant of leave when you assess this
