Extended limited tax liability

• they were subject to unlimited income tax liability for at least five years in the last ten years prior to the end of their unlimited tax liability,
• they become or are resident in a low-tax country, and
• they have substantial economic interests in Germany.

• "Low-tax countries" are, for example, certain cantons in Switzerland, the United Arab Emirates, Singapore, Hong Kong, Bulgaria, Hungary, Paraguay, Bolivia; but also countries where there is "remittance-based taxation," i.e., where one receives a kind of preferential tax treatment for foreign income. Overall, the point is that a country levies less than two-thirds of the German income tax burden (in 2025 approx. <18.55%).
• Substantial economic interests are, for example:
  • a shareholding of more than 1% in a German corporation
  • a share in a German partnership
  • domestic income of more than 30% of total income or more than 62,000 euros
  • German assets of more than 30% of total assets or more than 154,000 euros.

The ETF portfolio and extended limited tax liability

• has more than €62k in income per year from the portfolio (capital gains)
• or has more than €154k in total assets in the German ETF portfolio.

1. Inform their custodian bank that they have moved away and that the account should therefore be marked as "tax-exempt" – some banks do not offer this at all and one has to close the account anyway. Then the question of whether to keep the German account or not becomes moot.
2. Assuming the custodian bank marks the account as tax-exempt – only then does one have to ask oneself whether to keep the ETFs in the account or transfer them to a foreign account.
3. With a German account, the probability seems higher that the tax offices will "look at" the positions and the whole debate about the extended limited tax liability mentioned above begins.

Summary

• If you want to absolutely minimize the risk of having any discussions with the tax office regarding extended limited tax liability on your capital gains after your move, then transfer your ETFs and stocks to a foreign securities account (see below).
• If you would rather keep your positions in your German account, e.g., because you find German banks more trustworthy than other banks (which can certainly be relevant), then leave your ETFs and stocks in your German account.

• Interactive Brokers seems to be recommended by far the most often – low fees and almost all countries worldwide are supported as places of residence. Apparently, it is also the case that accounts held by US firms do not (?) fall under the automatic exchange of information between the USA and Germany, so if you are particularly paranoid about possible questions from the tax office, that could be an argument for Interactive Brokers. However, I do not know how relevant that may be in reality.
  Account management is free of charge and transaction costs only apply to purchases and sales. It is only a securities account, so you do not get a bank account here.
• Swissquote is rarely mentioned but is probably a solid second choice. Attention, the corporate structure of Swissquote has been somewhat confusing since the acquisition of Internaxx: There is the "Swiss" Swissquote with headquarters in Switzerland; this is the "original" version, which is likely less relevant for most people as the fees there are significantly higher. And then there is Swissquote Luxembourg, which was originally another bank with a different name (Internaxx) that was explicitly aimed at expats. I strongly suspect that Swissquote Luxembourg (= Internaxx) is likely the better choice for most people's purposes, as the fees are lower. Theoretically, one also gets a bank account in Luxembourg there, which can also be practical, especially for people whose German bank does not allow for the continuation of the account abroad.
  Account management is free while living in the EU, but then costs €15 / month in most other countries.