@eily-cournoyer
1. generally, he would be considered a resident for Tax purposes from the first day he was in the USA ( so , absent any other issues ), it would be the day he entered US with the GreenCard ( admission date ) -- often printed on the GreenCard.
2. Thus ( and again absent any other contravening factors ), he would have been a Non-Resident Alien prior to this admission date and therefore he would be taxed on world income ONLY from the admission date. So his earlier income is foreign source income and therefore not taxable to the US. Thus his self-employed income in the UK may not be pertinent for UDS tax purposes.
3. From what you said so far , I think it may be simpler for you two to file as married filing separate --- i say this because (a) while you have a full year residence in the USA and can use the standard deduction, his residency start date would be the date of admission and thus he will have to use itemized deduction..
(b) The way around this would be to request to be treated as a resident for the whole calendar year , including his foreign income for the whole year ( eligible for exclusion under FEIE under US-UK tax treaty ) and all the complications that this will entail.
Note also that self-employment income of a US person would require SECA tax for the year ( unless he can show a certification of participation from the UK and therefore no requirement to pay to the US.
Hope this helps.
Is there more I can do for you ?
