Before you start — the filing trap, and a death mid-year
Two things worth knowing before opening the form itself: how it has to be filed, and that a deceased person's residence isn't worked out the same way as a living one's.
It can't be e-filed through HMRC's free service
HMRC's own 2025–26 notes state it directly: do not submit the SA109 pages as an electronic attachment to an online filed tax return through HMRC's free Self Assessment service.
Filing it means commercial Self Assessment software, a professional agent, or paper — and paper filing means the earlier 31 October deadline, not 31 January.
The form's new name, for the same tax year the remittance basis ended
For 2025–26 the form is titled 'Residence and foreign income and gains (FIG) regime etc', not 'Residence, remittance basis etc' — because the remittance basis it used to be named for was abolished from 6 April 2025.
The GOV.UK web address still uses the old name; the form and its notes don't.
A death mid-tax-year needs separate guidance
If SA109 is being completed on behalf of someone who died during the 2025–26 tax year, HMRC's notes point to a different guidance path — RFIG20900 onwards — to establish that person's residence status.
This is not the standard Statutory Residence Test applied to a shortened year; treat it as its own question.
Two things worth knowing before opening the form itself: how it has to be filed, and that a deceased person's residence isn't worked out the same way as a living one's.