@alainncat , as I see it
1. Your ideal ( what you appear to be trying to achieve);
(a) For US Tax purposes -----> Keep US residency valid for the whole calendar year of 2025 -- so you get to use the standard deduction; exclude Irish earnings from US tax ( exclusion or foreign tax credit).
(b) For Irish Tax Purposes ---> Exclude US income by claiming Irish Tax residency only from the day of arrival.
2. For the basics ---- you can be a resident of one country ONLY at a time; the purpose of tie-breaker rule/ regime is to determine a winning residency i.e. one residency for the "pertinent " tax year. Note that each country has its own definition of Tax Year --- for US ( and incase of Non-Immigrant / Citizen ), there are rules for start and end of the "tax year" -- "Dual Status" Tax Payer; For Ireland there is "Split-Year" -- as I ref'd in my earlier post. The foregoing would generally limit your "Double Taxation" clause / benefits ONLY to incomes that are taxed by both countries -- from your post , it would appear to be the US-sourced in come POST your residency start in Ireland ( US taxes you on US sourced income and Ireland taxes you on world income, including the US sourced and Taxed income).
3. The only way I see this working out ( and it may not be worthwhile and/or even doable ),:
(a) you continue to have substantial financial and other connection to the USA for the whole of 2025, thus using "substantial interest/ connection" -- home, financial , Driver's license, intention to return etc. etc.
(b) you are temporarily residing in Ireland , for employment etc. and therefore not a resident and have no intention of residency. This implies a temporary foreign assignment by your US based employer to a local subsidiary or similar. Note that from my reading of Irish residency , it appears to be intention based and finalized only after staying there for a significant period and declaration of intention ( unlike US where it is a fixed number of days of presence ).
My general conclusion is for you to just accept the facts as they are -- i.e. you are a Dual Status Tax Payer in the USA for the Calendar/ Tax year 2025 and a "potential " resident of Ireland for the period of presence in the Ireland. I do not believe that it would be worth your while to claim a full calendar year resident for the USA , just for the sake of deduction. It opens up too many ands/ifs/buts and unless facts bear out, an impossible mountain to sustain.
Is there more I can do for you ?
