A Florida residency claim is, at its core, a documentation claim. The driver’s license, the Declaration of Domicile, the homestead exemption, the updated estate plan — all of these are inputs to one underlying assertion: that the taxpayer was physically present in Florida for the majority of the year and has built the life-anchors of a Florida domiciliary.
When the New York Department of Taxation and Finance, the California Franchise Tax Board, or the New Jersey Division of Taxation challenges that assertion, they do not start by reviewing paperwork. They start by reconstructing where the taxpayer actually was, day by day, for the years in question. And they do this from data sources the taxpayer typically does not control.
Most people who establish Florida residency cannot match the granularity of that reconstruction. Not because they did anything wrong — but because the record they kept was never built to be tested against a forensic timeline.
Today, Southbound is available on the App Store. It exists because the gap between how taxpayers track their days and how auditors verify them is wider than most people understand, and because closing that gap is a documentation problem that contemporaneous tracking can solve.
This post is about the problem, not the product. The product is what falls out of taking the problem seriously.
How Auditors Reconstruct a Day Count
A residency audit at the high-income level is a forensic exercise. The state’s objective is to assemble an independent timeline of the taxpayer’s physical location for every day of the tax year, then compare that timeline to what the taxpayer claimed.
The data sources used to build that timeline are well-documented in published audit guidance and in cases that have reached administrative appeal:
- Cell phone records. Carriers retain location data, including cell tower connections and approximate geolocation, for periods that vary by carrier but typically extend back several years. New York’s Nonresident Audit Bureau routinely subpoenas this data in contested cases.
- Credit and debit card transactions. Every swipe carries a merchant location. A coffee purchase in Manhattan on a day the taxpayer claimed to be in Palm Beach is a problem that is difficult to explain after the fact.
- EZ-Pass and toll transponder logs. These records show vehicle entry and exit at specific bridges, tunnels, and toll roads, with timestamps. They are particularly damaging in New York audits because they place the taxpayer’s vehicle inside the state on dated, time-stamped intervals.
- Building entry logs and doorman records. Co-op and condominium buildings frequently maintain visitor and resident entry logs that auditors have successfully subpoenaed.
- Airline and rail manifests. Travel records establish entry and departure dates that bracket presence in a state.
- Social media activity with location metadata. A geotagged photograph on Instagram or Facebook can place the taxpayer in a specific city on a specific day.
Once the auditor has assembled this independent timeline, the taxpayer is asked to explain inconsistencies and to produce contemporaneous records that corroborate the days they claim were spent in Florida. In New York, the taxpayer bears the burden of proving the day count, and the evidence must be clear and convincing.
This is not a hypothetical framework. The mechanics of day-by-day reconstruction have been litigated and refined over more than a decade of administrative decisions, particularly in New York. The standard is exacting.
Why Common Tracking Methods Fail
Most taxpayers who claim Florida residency rely on one of three approaches to track their days. All three fail under audit pressure, and they fail for the same underlying reason: the record was not contemporaneous, granular, or location-anchored at the point of capture.
Calendar Reconstruction
A taxpayer reviews their calendar at year-end and counts the days that appear to involve Florida activity. This produces a number, but the number is built on inference. A calendar entry that says “dinner at the club” on a Tuesday in March does not, by itself, establish which state the taxpayer was in. Calendar entries also tend to omit travel days, half-days, and informal stays.
Under audit, calendar-based counts are routinely contradicted by independent data. Auditors do not weigh self-prepared calendars heavily.
Spreadsheet Tracking
A more disciplined approach: a spreadsheet maintained throughout the year, with one row per day, marked Florida or non-Florida. This is better than reconstruction, but it has two failure modes.
First, the entries are still self-reported. There is no independent verification that the taxpayer was actually in the location they recorded. An auditor who finds a credit card transaction in Greenwich on a day the spreadsheet says “Palm Beach” has located a problem that the taxpayer must now explain.
Second, spreadsheets degrade. Most people who start them in January are inconsistent by April. Gaps appear. Days are filled in retroactively. The contemporaneous nature of the record — which is what makes it credible — erodes.
Memory and Travel Receipts
The weakest approach: relying on travel receipts, hotel bills, and recollection to reconstruct the year if challenged. This produces partial coverage. It establishes specific high-confidence days (the day a flight was booked, the night a hotel was paid for) but leaves long stretches unaccounted for. Auditors fill those stretches with their own data, which is rarely favorable to the taxpayer.
What a Defensible Record Actually Looks Like
The administrative case law and practitioner guidance converge on a consistent definition of an adequate residency record. The record should be:
- Contemporaneous. Captured on or near the day in question, not reconstructed afterward.
- Granular. Resolved to the day, not the week or the month.
- Location-anchored. Tied to verifiable location data, not self-described intent.
- Complete where possible. Covering as much of the tax year as you can, with any gaps shown and not inferred.
- Auditable. Capable of being produced as evidence and corroborated against independent data sources.
Traditional methods — calendars, spreadsheets, receipts — fail one or more of these criteria. The taxpayer who maintains a contemporaneous, location-anchored, day-resolution record of presence has a fundamentally stronger position than the taxpayer who reconstructs after the fact, regardless of how much paperwork the latter has filed.
This is the standard the audit process tests against. It is the standard most residency records do not meet.
Where Southbound Fits
Southbound is a Florida residency day tracker for iPhone. It records location in the background using iOS’s significant-location-change service, marks recorded days as Florida or non-Florida from the device’s location, and keeps a running record that the taxpayer can review and correct.
The design choices follow directly from the problem:
- Location-anchored. From the install date forward, a location-derived day comes from where the device was, not what the user remembered later. Days entered through the Catch Up wizard are flagged as user-supplied, and later days can also be entered or corrected manually and are labeled accordingly.
- Contemporaneous capture. From the install date forward, the record is built as location updates arrive, and the PDF shows gaps.
- No vendor copy of location history. Data is stored on the user’s iPhone and synced to their personal iCloud account via Apple’s CloudKit. Southbound runs no servers that can see it, maintains no accounts, and does not receive the data. The app has no advertising, no ad trackers, and no third-party analytics SDK.
- Inverted framing. The primary metric is the Departure Budget: how many days remain that the taxpayer can spend outside Florida while staying within the budget for their chosen Florida-day goal. This reframes the question from “did I do enough?” to “how much margin do I have left?”, which is the operationally useful version.
For taxpayers whose former state has the resources and motivation to audit — New York, California, New Jersey, Connecticut, Illinois, Massachusetts — the cost of inadequate documentation is asymmetric. A clean audit that closes with no change costs nothing. A contested domicile audit, as documented in The Real Cost of a State Tax Residency Audit, can run $100,000 to $300,000 in professional fees and take three to five years to resolve. Contemporaneous records are the cheapest insurance against that outcome.
What Happens When Southbound Is Installed Mid-Year
Most taxpayers who arrive at residency tracking arrive late. The realization that the year started on January 1 and the record did not is common. The practical question is what the app can do for the months that have already passed.
The honest answer has two components — and the distinction between them matters, because they sit at different levels of evidentiary weight.
Going forward, the record is contemporaneous from the install date. From the moment Southbound is installed, the location capture begins. For the remaining portion of the tax year, the taxpayer has a contemporaneous record based on collected location checks, with manual entries and gaps identified.
For the months already passed, Southbound provides a Catch Up wizard. The user enters date ranges for any trips they took outside Florida during the elapsed portion of the year. The app computes Florida days for the prior period as days-elapsed minus days-entered-as-trips. Days the user does not account for default to Florida. The result is a starting balance for the year’s day count and an accurate Departure Budget from the install date forward.
The Catch Up wizard is the right tool for the bookkeeping job. It produces a coherent year-to-date number, anchors the contemporaneous record against a known starting point, and lets the Departure Budget reflect days already spent.
It is not, however, the same kind of evidence as the contemporaneous record, and it should not be presented as if it were.
The Catch Up entry is self-reported. The taxpayer types in the trips; the app records what the taxpayer said. Against the standard described earlier in this post — contemporaneous, granular, location-anchored, continuous, auditable — the Catch Up entry is granular and continuous, but it is not location-anchored in the third-party-verified sense, and it is not auditable on its own. It carries roughly the evidentiary weight of a spreadsheet entry made retroactively: useful, but corroborable only against independent records the taxpayer produces alongside it.
The practical implication for a mid-year-installed taxpayer is straightforward. The going-forward record is contemporaneous, and an auditor can still test it against other evidence. The Catch Up portion should be treated as a starting balance to be corroborated, not as standalone documentation. For an audit covering the pre-install months, the taxpayer would lean on the same evidence anyone in that position would lean on: credit card transactions, travel itineraries, hotel confirmations, calendar entries paired with corroborating documents, toll records requested from the operator. The Catch Up entry is a useful index against which to organize that evidence; it is not a substitute for it.
That framing leads to the part most worth being clear about.
The Catch Up wizard does not change the taxpayer’s residency status for the period it covers. Installing Southbound in May does not affect actual residency for the prior four months in either direction. It only produces a self-reported starting count for those months. The taxpayer’s residency status is a function of where they actually were and what life-anchors they actually maintained, not of what tool they later used to record it.
The corollary is worth stating plainly. Selective entry into the Catch Up wizard — omitting non-Florida trips the taxpayer actually took, to inflate the Florida count — is the kind of behavior that converts a routine residency dispute into a fraud inquiry if the omitted travel surfaces in independent records. Auditors have access to credit card geolocation, EZ-Pass logs, airline manifests, and cell tower data; they will compare claimed presence against what those independent sources show. A clean Catch Up record of two trips, when the taxpayer actually took five, is not a recordkeeping problem. It is a much larger one.
For taxpayers whose actual physical presence supports the residency claim, an honest Catch Up entry plus a contemporaneous going-forward record is a meaningful documentation improvement over no record at all — and over a calendar or spreadsheet maintained on the side. For taxpayers whose actual physical presence does not support the claim, neither tool helps, and using either to produce a desired result is the wrong approach.
For prior tax years — a year already closed, where the taxpayer is facing or anticipating an audit — the appropriate response is to consult a tax attorney before producing any reconstructed record. The Catch Up wizard is designed for the current year. Reconstructing closed years is a different exercise that warrants professional supervision.
What Southbound Does Not Do
Southbound is a documentation tool, not a residency strategy. It does not advise on domicile. It does not file paperwork. It does not replace the work of a tax attorney, a CPA, or a residency planning professional. The 183-day count is a floor, not a ceiling, and presence alone is not sufficient to establish or defend Florida domicile.
What Southbound does is produce the underlying day-by-day record that every other component of a residency strategy depends on. The driver’s license, the homestead exemption, the Declaration of Domicile, the updated estate plan — all of these assume that the taxpayer can demonstrate physical presence when challenged. Southbound makes that demonstration possible.
Available Now
Southbound launched on the App Store on April 27, 2026. Update, October 2, 2026: the free launch period ended on September 15. New downloads start with a 14-day free trial for eligible users. iPhone only. No accounts, no Southbound servers; data is stored on the user’s iPhone and backed up to their personal iCloud.
Download Southbound on the App Store
The 183-day question is not, fundamentally, a question about days. It is a question about evidence. The taxpayer who can produce a contemporaneous, granular, location-anchored record of presence has answered it. The taxpayer who cannot has not — regardless of how many days they actually spent in Florida.
Build the record while the year is happening. The cost of doing so retroactively, under audit pressure, is several orders of magnitude higher.
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Southbound
Published Apr 27, 2026