Stayline, support
Stayline counts the days you spend in each country: the Schengen 90/180 rule, tax residency thresholds such as 183 days, the UK and US day tests, and any visa limit you set. It works offline, with no account, and everything stays on the iPhone.
Getting help
Write to contacttheomartin@gmail.com. I built the app and I read every message myself. Telling me the trips involved and the number you expected makes a counting question answerable on the first reply.
How days are counted
Schengen. On any day, Stayline looks at the 180 days ending that day and counts every day you were in a Schengen country, arrival and departure days included. More than 90 is an overstay. Days in Ireland, Cyprus and the UK don't count. Monaco, San Marino and Vatican City are counted as Schengen because they are entered through France or Italy.
Travel days. A day you travel counts for both countries, unless a limit is set to count only where you are at midnight, as the UK statutory residence test does.
The US substantial presence test adds this year's days, a third of last year's and a sixth of the year before, and also needs 31 days this year.
Stayline is not legal or tax advice. Rules have exceptions the app cannot know about. It counts from the dates you enter, so check them against your own records before a decision that matters.
Worth knowing
Check in uses your location once, while the app is open, to find the country. If location is off, choose the country from the list instead.
Future trips are plans: add them like any trip, and the Schengen card warns you if they would take you over 90 days.
Pro adds tax and visa limits, PDF and CSV reports and alerts. Restore purchases is in Settings. Nothing is on a server, so there is no account to recover and no history to restore on a new phone unless your iPhone backup carries it.