I didn't know, not filling in W-8BEN will stop the broker from withholding 30% DWT. Generally tax authorities take the worst case and tax us maximum and then we need to file to prove that we are eligible for lower tax. So this broker not witholding 30% for not filling W-8BEN doesn't make sense to me.
It doesn’t make sense, but we’re talking about automated systems and humans who program them. If somebody forgot an “IF..THEN,” then improper withholding results. And that’s bad, because it turns into your problem, and with a
very twitchy broker once the problem is discovered that’ll not hesitate to try to clean up the mess. You do not want any of this, trust me.
Also, there are some rare cases when not having a W-8BEN on file can cause some significant other problems. I looked them up once and don’t remember them off the top of my head, but there are some such cases. I think it has to do with KYC-related problems that in rare cases can end up in asset freezes.
....Do this by the book, please! You’re dealing with big amounts of money, typically, and it’s not something you should fool around with. File a truthful W-8BEN (or W-9 if a U.S. person), and keep it current if something on the form changes, like your country of residence.
In any case we are not under US law.
No, but your money is. Interactive Brokers is a U.S. broker. I happen to know that you also invest in U.S. listed/traded funds and stocks. That part of your wealth is under U.S. law, too, regardless of which broker arranged those positions.
This works in reverse, too. If you live in France and hold some ES3 (STI fund), CPF assets, and a HDB unit, all three of those pieces of wealth are under Singapore law. (And with tax considerations in France since you’re a resident of France.) Singaporean authorities will not hesitate to do whatever they want to do under Singapore law. Their wealth playground, their rules.