Federal tax gets the attention. State tax generates a disproportionate share of the confusion, because there isn’t one system — there are many, they don’t agree with each other, and the situations that trigger obligations are frequently ones people don’t recognize as significant.

What creates an obligation

Broadly, a state can tax you on two bases: because you live there, or because you earned income from a source within it.

Residency generally makes all your income taxable by that state, regardless of where it was earned.

Source income makes income connected to that state taxable there even if you’ve never lived in it — property located there, work physically performed there, or a business operating there.

Which means one stream of income can be within the reach of two states at once. This is the root of most multi-state confusion.

Situations people don’t expect

Moving mid-year. You’ll likely file part-year returns in both states, splitting income by when it was earned relative to the move. The complication is that the split isn’t always obvious — deferred compensation, a bonus paid after the move for work performed before it, or investment gains realized around the transition.

Working remotely across a state line. If you live in one state and your employer is in another, which state taxes the income depends on both states’ rules — and they may not be consistent with each other. Some states assert taxing rights over remote workers of in-state employers in ways that surprise people.

Rental or investment property elsewhere. Property producing income in another state usually creates an obligation there, whatever your residency. This includes property you inherited and have never visited.

Business operating across state lines. Selling into, employing in, or having property in a state can create obligations. Thresholds vary, and remote sales in particular have shifted considerably.

Travelling for work. Some states assert taxing rights over income earned during even brief periods physically working there. Enforcement varies enormously, but the rule exists.

Residency is not simple

The intuitive definition — where you live — is not the legal test, and the tests vary by state.

States generally look at some combination of physical presence over a period, where your permanent home is, and a broader assessment of where your life is centred: family, professional licences, vehicle registration, voter registration, banking, medical care.

Two consequences follow.

You can be treated as a resident of two states. They apply their own tests independently, and both can conclude you qualify. Mechanisms usually exist to relieve the resulting double taxation, but they’re claimed on a return rather than applied automatically.

Leaving is harder than arriving. States with significant tax revenue at stake tend to scrutinize departure closely. Keeping a home, returning frequently, or maintaining professional and financial ties can support a conclusion that residency never actually ended — sometimes years later.

If you’re changing state residency deliberately, document it. The evidence is much easier to assemble at the time than to reconstruct under examination.

Relief from double taxation

The general mechanism is a credit: your resident state gives credit for tax paid to another state on the same income, so the same dollars aren’t fully taxed twice.

Important qualifications. The credit is usually limited to what your resident state would have charged on that income — so if the other state’s rate is higher, you don’t recover the difference. The rules are state-specific. And critically, the credit has to be claimed. Both returns have to be prepared correctly and in the right order for it to work.

This is where a return prepared without attention to the multi-state interaction goes wrong. Each return may look fine independently while the credit is understated or missed entirely.

Reciprocity

Some neighbouring states have agreements simplifying matters for people who live in one and work in the other — typically allowing you to be taxed only by your home state, with withholding adjusted accordingly.

Where these exist they’re genuinely helpful. But they’re specific to particular state pairs, they usually require filing a form with your employer, and they generally cover only employment income. They’re worth checking for and worth not assuming.

Practical suggestions

Say something. Tell your preparer about a move, a remote arrangement, property elsewhere, or a period working in another state. These aren’t visible on income documents.

Check your withholding after any change. Moving or changing to remote work frequently leaves withholding pointed at the wrong state. Discovering that at filing means an unexpected balance in one state and a refund in the other.

Document a residency change. Contemporaneously, not later.

Don’t assume no return means no obligation. Filing requirements can exist below the level at which tax is actually due. A missed filing obligation is a different and more annoying problem than a small balance.

Prepare them together. Multi-state returns interact. Preparing them as separate exercises is how credits get missed.

Worth the conversation

Multi-state situations are among the most common places we find errors in returns prepared elsewhere — usually not carelessness, but a preparer treating each state in isolation.

If your situation touches more than one state, it’s worth a specific conversation rather than an assumption that it’s handled.

This article is general information, not tax advice. State rules vary considerably and change — get in touch to talk about your circumstances.