ProofstayAbout Proofstay
It started with a friend's day count.
A friend of mine had to keep track of how many days they spent in each place, because a rule in their life depended on it. The count was kept by hand, never quite certain, and if anyone ever asked, my friend would have to show where they had been, day by day.
I'm Hoang Chu, a solo developer. I built Proofstay for my friend: an iPhone app that notes where you are each day, keeps that record so it can't be quietly changed, and does the counting for you. Then it became clear how many people live with the same kind of count: Schengen's 90 days, a state's 183, the UK's midnights, a snowbird's winter. So I made it public.
That is still the whole idea. Proofstay proves where you were, and for how long. The counting is there because it needs the days anyway.
Before a rule ships
The count has to be right
A day-count app that is off by one day is worse than no app. So every rule goes through the same checks before it reaches the app or a calculator on this site:
- Worked examples, written down first. Each rule (Schengen 90/180, the US Substantial Presence Test, the 182-day visitor limit, Ontario's OHIP, the UK Statutory Residence Test day count, 183-day state and country counts) has a set of test cases with known answers.
- One set of cases, two code bases. The same cases run against the app's Swift code and this website's TypeScript code, so the app and the calculators can't drift apart.
- Against the official tool. The Schengen count was compared with the European Commission's short-stay calculator: 10 of 10 scenarios gave the same answer.
- The awkward days. Leap years, trips across New Year or across 6 April, overlapping trips, and every band edge of the UK ties table.
- Saying what it can't know. Domicile, the UK work tests, a closer connection: where a rule turns on facts a day count can't see, the app and the calculators say so instead of guessing.
Where your days live
On your phone, not with us
Where you have been is personal, so Proofstay is built to never hold it. Places are worked out on the iPhone, offline. There is no account to create and no server with your days on it; the optional backup goes to your own private iCloud. The app carries no analytics and no tracking SDKs, and your full history can be exported as CSV and as the raw proofed log at any time, whether you pay or not. The calculators on this site run in your browser and send nothing anywhere. Details are in the privacy policy.
The guides on this site
Sourced, dated, and corrected when wrong
Each guide states the rule in plain words, links the official source next to it (IRS, HMRC, the European Commission, state and provincial governments), and shows the date it was last checked. Numbers in the examples are produced by the same tested rule code as the app. When a rule changes, the page changes with it.
Proofstay is a record-keeping tool and a planning aid. It doesn't give tax, legal or immigration advice, and it doesn't promise that any authority will accept its report.
Spotted a mistake, or need a rule that isn't covered yet? Write to me at support@proofstay.app. Hoang