How should I track tax residency days?

The safest starting point is a record you can explain later: each day, the jurisdiction you were in, the evidence that supports it and any unusual circumstance worth noting. Do this while the details are fresh. Reconstructing a year from memory when a threshold is already close is much harder.

Use the right period for each place

Do not assume every jurisdiction follows the calendar year or the same day-counting test. The UK and US guidance show how different official systems can be. Create separate review windows where necessary, then check the current rule for the jurisdictions that matter to you.

Keep evidence outside the app too

Passports, tickets, accommodation records and work records may be useful if a professional needs to review the timeline. A tracker can make the chronology easier to manage; it is not the evidence itself and it cannot decide which legal exception applies.

How Flags Tax helps

Flags Tax can help you keep a private day record from photo metadata and manual confirmation, then flag a jurisdiction for review. It is deliberately an early-warning tool rather than tax advice. For the US-specific limits, see the substantial presence test, or run your numbers in the free substantial presence test calculator.