How do you prove how many days you spent in a country?

Border records come first. A stamped passport is the traditional form, and automated entry/exit recording is replacing it at EU external borders — which cuts both ways. It removes the ambiguity of a missed stamp, and it removes the assumption that an unstamped trip went uncounted.

Travel documents come second. Boarding passes, e-tickets and airline account histories establish direction and date, and they survive a lost passport. Their weakness is that a booked flight is not a boarded one, so they corroborate rather than prove.

Financial and life records come third, and they are underrated. Card transactions, ATM withdrawals, mobile roaming bills, payroll, tenancy agreements, utility bills and insurance all place you somewhere on a date. Individually weak, collectively hard to dispute — and unlike stamps, they are generated continuously without you doing anything.

Most people start this exercise years late. It is recoverable, in roughly this order:

1. Passport stamps first. Photograph every page, including expired passports. Transcribe into a list of dates and directions, and note where a stamp is missing rather than guessing past it.
2. Airline and booking accounts. Most retain years of history and will export it. This usually fills the majority of the gaps stamps leave.
3. Card and bank statements. Filter by foreign-currency or merchant location to place yourself on specific dates.
4. Photo libraries. Location metadata is dated and precise, and it covers the days no institution recorded.
5. Email. Confirmations for hotels, trains and car hire pin down dates the other sources miss.

Then reconcile. Where two sources disagree, note it rather than quietly choosing the more convenient one — an explained discrepancy reads as diligence, an unexplained one reads as reconstruction.

The harder version of the question, and the one settlement applications turn on. You cannot produce a record of an absence, so the argument is made positively: evidence that you were continuously somewhere else. A tenancy running the whole period, uninterrupted payroll, a child in school, utility usage — these establish a life lived in one place, which is a stronger answer than the absence of an entry stamp.

• Regulation (EU) 2017/2226 — Entry/Exit System (EES)
• HMRC — RDR3: Statutory Residence Test, records you should keep
• USCIS — Policy Manual, Volume 12: continuous residence and physical presence