Tax residency is decided in hindsight. Most countries fix your status from a physical-presence day count, and you only "discover" you crossed the line after the year closes and the number is locked. A tax residency day alert app flips that around: it fires a proactive notification before you hit a threshold, while you still have the option to leave. This guide shows the warning ladders for the 183-day rule, Schengen 90/180, the US Substantial Presence Test and individual US states, and how to set them all up on your iPhone.
Why passive day counters catch you too late
Most day trackers are really just spreadsheets with a nicer interface. They tell you where you stand if you remember to open them. The problem is that residency thresholds do not announce themselves. You cross the Schengen 90-day line, or the 183rd day in a country, on an ordinary travel day when checking a counter is the last thing on your mind. By the time you notice, the day is already logged and the count cannot be undone.
The fix is to make the count come to you. A proactive local notification that says "7 days of Schengen allowance left" arrives when it can still change a decision - to book a flight out, to move a trip, or to stay put. That early warning is only as reliable as the day data underneath it, which is why pairing alerts with automatic location tracking (so days log themselves) is the difference between a real safeguard and a reminder you will ignore.
Ladder 1: the US Substantial Presence Test
The IRS treats you as a US resident for tax purposes if you meet both parts of the Substantial Presence Test in a calendar year:
- 31 days present in the current calendar year, and
- 183 weighted days across a three-year window, counting the current year at 100%, the first preceding year at one third, and the second preceding year at one sixth.
A day of presence is any day you are physically in the US at any time, though the IRS excludes some days (commuter days from Canada or Mexico, transit under 24 hours, certain medical-condition days, and exempt individuals such as some visa holders). The two binding numbers are 31 and 183 weighted. The app tracks the weighted count in real time and can warn you as your remaining days shrink, at configurable tiers such as 90, 45, 21, 14, 7 and 3 days left. Those tiers are the app's early-warning design, not an IRS rule - the government only cares about the final 31 and 183.
Ladder 2: Schengen 90/180, now with automated enforcement
Non-EU visitors may spend at most 90 days in any rolling 180-day period across the whole Schengen Area. The 180-day window is genuinely rolling: every day it looks back 180 days and recounts. Leaving does not reset anything - days are only "returned" as they drop off the back of the window. And both the entry day and the exit day count as full days, so short hops add up faster than people expect.
This is exactly the kind of moving target where a proactive alert earns its keep, and the stakes just rose. The EU's Entry/Exit System (EES) began its phased rollout on 12 October 2025 and reaches full operation on 10 April 2026, using biometrics to detect overstays automatically at external borders. The related ETIAS travel authorisation (around 20 euros, valid three years) is expected to launch in Q4 2026 and become mandatory after a transition period. Overstays can trigger fines and entry bans. Manual day-math is precisely what EES removes tolerance for, so the app warns you as you approach the 90-day line rather than after you have crossed it.
Ladder 3: individual US states
State residency does not follow a single national number, so a per-state ladder matters. The app carries a bundled dataset of statutory thresholds and warns ahead of each one:
- New York treats you as a statutory resident if you keep a permanent place of abode for substantially all of the year (roughly 11 months) and spend more than 183 days in the state. Any part of a day in New York counts, including transit days.
- California has no fixed day count. It applies a facts-and-circumstances "temporary or transitory" test, with a nine-month presumption of residency and exposure that can begin earlier. States with no bright-line day test are flagged in the app as facts-and-circumstances rather than given a false number.
- The most aggressive audit states - New York, California, New Jersey, Massachusetts and Illinois - each carry their own limit, and the alert respects the per-state figure rather than a global 183.
Custom per-country thresholds
Beyond the built-in ladders, you can set your own day cap for any country: a tax-treaty tie-breaker count, a national 183-day residency line, or a self-imposed safety margin below the real limit. Day rules are far from uniform, which is exactly why a flexible custom threshold is useful. The UK Statutory Residence Test is a good illustration: 183 days makes you automatically UK resident, while fewer than 16 or 46 days can make you automatically non-resident depending on your prior-year status, with a sliding day-count-versus-ties matrix in between. No single number captures that, so the app lets you encode whatever line actually governs you.
Two settings that decide whether the warning is even right
An alert is only as accurate as the count it watches, and two settings shape that count:
- Day-counting mode. Regimes disagree on what a day is. The US test and New York count any part of a day; others count midnights or require full days. The app offers four modes - Calendar Day, Midnight Rule, Full 24-Hour Day and Overnight Stay - so the warning matches the count that actually applies to you.
- Custom tax-year start. Not everyone runs January to December. The UK tax year starts on 6 April, and others vary. If the count resets on the wrong date, every warning downstream is off, so alerts are computed against your configured tax-year boundaries.
Setting up threshold alerts in the app
Tax Residency Tracker is built around getting the warning to you in time. A sensible setup order:
- Grant notification permission so local alerts can fire from the device.
- Turn on automatic GPS tracking. Background border and US-state detection creates dated stays for you, even when the app is closed, so the alerts sit on real day data instead of something you had to remember to log.
- Enable the built-in ladders you care about - the Substantial Presence Test, Schengen 90/180, and your home-state statutory limit - each of which warns you as you approach its threshold.
- Add custom per-country thresholds for treaty day-counts or self-imposed caps.
- Confirm your day-counting mode and custom tax-year start so the count, and every warning built on it, matches your situation.
- Set your daily reminder time. If you would rather not show country or day detail on a locked phone, turn on discreet mode, which replaces the notification text with a generic reminder.
Everything runs locally. The alerts fire on-device with no account and no server, fully offline, and your travel history stays on your phone with optional iCloud sync through your own private account. If you want to test a plan before committing, the planned-stays preview lets you add a future trip and see the projected Substantial Presence Test, Schengen and country totals before you book, and CSV export with attached document proof hands your accountant an evidenced record if you ever need it.
Frequently asked questions
Do the alerts run in the background and offline?
Yes. Alerts are local notifications that fire from your iPhone with no account and no server, so they work fully offline. Because they pair with background GPS detection, your day counts update and your warnings arrive without you opening the app.
Is the 90/45/21/14/7/3 warning ladder an official rule?
No. Those tiers are the app's configurable early-warning design. The only binding numbers for the US test are 31 current-year days and 183 weighted days; the ladder simply gives you runway before you reach them. The same applies to the Schengen "as you approach 90" warnings.
What is discreet mode?
Discreet mode hides the specifics on your lock screen, showing a generic reminder instead of the country and remaining-days detail. It is handy if you would rather not display border or residency context on a locked phone at a checkpoint.
Will alerts match countries that count days differently?
Yes, if you set the right mode. The app supports Calendar Day, Midnight Rule, Full 24-Hour Day and Overnight Stay counting, and a custom tax-year start, so the warning reflects the count that actually governs you rather than a generic January-to-December calendar.
Next, see the best app to track days in a country for taxes, the Substantial Presence Test calculator, the Schengen 90/180 calculator, or browse all guides.