The first tax season abroad is where the gap between feeling settled and actually being settled becomes obvious. You have an apartment, a local SIM, a favourite noodle place — and absolutely no idea whether the country you live in expects you to file anything, or whether your home country still has a claim on the salary you're earning here. Most expats discover the answer late, usually in March or April, usually from a colleague who mentions it in passing. By then the paperwork window is already half closed.
Tax is the part of the move nobody plans for because it feels like Future You's problem. The trouble is that the rules turn on things you decide in your first months — how many days you spend in the country, whether you keep a property back home, which bank account your salary lands in — and by the time you understand them, you've already made the choices.
Residency is about days, not how you feel
The single concept that decides almost everything is tax residency, and it has nothing to do with your visa, your lease, or whether you call the place home. In most of Asia it comes down to a day count. Stay long enough and the country treats your worldwide income as fair game; stay below the line and it usually only taxes what you earned locally.
The thresholds are specific and worth knowing before you book that long trip home. Japan treats you as a non-permanent resident once you've lived there with an address for the year, and a permanent resident for tax once you've been there more than five of the last ten years — at which point your foreign income comes into scope. South Korea uses 183 days in a tax year as its residency trigger. Thailand also runs on 183 days, and since 2024 it taxes foreign income you remit into the country in the same year you're resident, which quietly upended a lot of retirement-and-remittance plans. Singapore is the outlier expats love: 183 days makes you resident, but it taxes on a territorial basis, so foreign-sourced income kept offshore generally isn't touched at all.
Here's the catch people miss. The day count is rarely "full days in the country" the way you'd assume — a day where you arrive at 11pm can still count as a day of presence. Border-hopping to stay under a threshold is a real strategy, but it's a fragile one, and immigration data now talks to tax authorities in more places than it used to.
The double-taxation trap, and the treaty that's supposed to save you
The fear that keeps people up at night is paying tax twice on the same money — once where they earned it, once back home. It happens, but less often than the panic suggests, because of double-taxation agreements. These are bilateral treaties that decide which country gets first claim and oblige the other to give you credit for what you've already paid.
Most of the obvious pairings are covered. Singapore alone has more than 90 such treaties; Japan, Korea and China all maintain broad networks. The mechanism is usually a foreign tax credit: you declare the income in both places but subtract the tax paid in one from the bill in the other, so you end up paying roughly the higher of the two rates rather than the sum.
The treaty does not file itself. You have to actively claim the credit, which means keeping every withholding statement, every local tax receipt, and often a certificate of tax residency that you request from your local authority. Lose those and the credit can be denied even though you genuinely paid — the burden of proof sits squarely on you.
And then there's the American exception, which deserves its own warning. The United States taxes its citizens on worldwide income no matter where they live, so the day-count rules above don't get a US passport holder off the hook. The Foreign Earned Income Exclusion shields roughly the first US$120,000 of earned income, and foreign tax credits handle much of the rest, but the filing obligation never disappears — and neither does the separate requirement to report foreign bank accounts over US$10,000 on an FBAR. If you're American, assume you file every single year, full stop.
The deadlines that sneak up on you
Even people who understand their residency get caught by the calendar, because every country runs on its own clock and almost none of them match the one you grew up with. Japan's individual filing window runs mid-February to 15 March. South Korea's general return is due in May. Thailand wants personal income tax filed by the end of March, with an extension into April for online filers. Singapore's deadline is 18 April for e-filing — and Singapore is unusually polite about it, sending you a reminder.
A few habits keep the deadline from becoming a crisis:
- Find out your country's tax year start the moment you arrive — Japan, Korea and Thailand run January to December, but the UK's runs April to April and Australia's July to June, which matters enormously when you're reconciling two systems.
- Ask your employer in month one whether they withhold and file on your behalf or whether that's on you. In Japan and Korea many salaried employees are covered by a year-end adjustment done by the company; freelancers and anyone with side income are not.
- Keep a single folder — physical or digital — for every payslip, withholding slip and bank statement from day one. The document you can't find in April is always the one from last August.
- If you moved mid-year, you almost certainly owe a part-year return in your old country too, and that deadline runs on the old calendar.
The freelancers and remote workers have it hardest. If you're being paid by a company in another country into a foreign account while living in Asia, you may owe tax where you sit even though nothing about the arrangement looks local. Thailand's remittance change hit this group especially hard, and "I get paid abroad" has stopped being the clean answer it once was.
When to stop doing it yourself
For a single salaried job in one country with company withholding, you can usually handle the filing yourself — the online systems in Singapore, Japan and Korea have improved enormously and most have an English path, even if it's buried. Pay for help the year anything gets complicated: the year you arrive, the year you leave, the first year you cross a residency threshold, or any year you have income in two countries at once.
Get a cross-border accountant rather than a purely local one for those years. A brilliant Tokyo tax adviser who has never touched a US return will not save an American from the IRS, and a London accountant won't know the Thai remittance rules. The fee for the messy years — often US$300 to US$1,000 depending on complexity — is cheap against a penalty for a return you didn't know you owed.
The expats who never panic about tax aren't the ones who found a clever loophole. They're the ones who spent an afternoon in their first month figuring out exactly where they stand, wrote the two deadlines on a calendar, and started the document folder before they had anything to put in it.