Form determination

Form determination is the core function of SPF: you provide the employee’s home and work locations, and SPF returns the withholding forms they’re required to complete. The rest of an SPF integration builds on that result.

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What you supply

Determination takes one home address and between one and ten work addresses. Those addresses do the heavy lifting; most of what SPF needs to know is derived from them. Three optional inputs adjust the outcome:

• Nexus: the states where your company has a business presence and is therefore subject to withholding obligations. Nexus is always assumed in a work state. For a resident state where the employee doesn’t work, you have to tell SPF. If you say nothing, SPF assumes nexus exists in the resident state.
• Lock-in letters: jurisdictions where the IRS has directed the employer to withhold at a specified minimum. A lock-in letter changes which forms and which paths the employee is offered.
• Interstate employee: a flag that fine-tunes outcomes for employees whose home and work states differ, mainly affecting whether certain Colorado and Oregon forms come back as recommended rather than optional.

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From address to jurisdiction

An address isn’t a jurisdiction. Turning one into the other is a real step, and for U.S. addresses it’s handled by the Symmetry Location Service. That last point is easy to miss. Determination doesn’t only decide which forms apply; it also supplies data those forms need. Pennsylvania forms require the PSD code and EIT rate for the address. Ohio forms need the school district. Indiana needs the county. All of it comes out of this step. Address normalization can also surface differences between what you submitted and what SPF resolved. See Address result codes for how to interpret those, and Address suggestions for how to present corrections to employees.

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What comes back

Once jurisdictions are resolved, SPF assembles the form set. In broad terms:

• The federal form is in scope by default. You can remove federal forms entirely (and the Federal section of Guided Mode along with them) by setting disableFederal to true in settings.json, in the SPF Registration JSON, or through the Admin Panel.
• The work state’s form applies, unless a reciprocal agreement removes the obligation and replaces it with an exemption certificate.
• The resident state’s form applies when it differs from the work state and that state taxes the wages.
• Local forms are added when the specific city, municipality, or school district imposes its own withholding.

Four things most often change this baseline: Reciprocity. When two states have a reciprocal agreement, an employee living in one and working in the other can ask to be exempt from work-state withholding and be taxed at home instead. SPF handles this by swapping the standard work-state form for that state’s reciprocal exemption certificate. Nexus. Without a business presence in the employee’s resident state, there may be no obligation to withhold there, which removes that state’s form from the set. Whether the resident state taxes out-of-state wages. Some states tax them always, some only when the work state doesn’t withhold, and some not at all. Local jurisdictions. Four states (Arkansas, Michigan, Oregon, and Pennsylvania) have cities and districts that publish their own withholding forms. Whether one applies depends on the specific municipality, not just the state, which is why a physical work address matters so much. The Multi-state scenarios reference has the full per-state table showing which states tax nonresidents, which tax out-of-state wages, and which reciprocal agreements exist.

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Recommended and optional forms

Not every returned form is mandatory. Each one is marked as recommended or optional. Recommended forms are the ones the employee should complete based on their situation. Optional forms are legitimately available to them but not required: an Oregon transit tax opt-in, for example, or Colorado’s DR 1059, the Affidavit of Exemption for the Nonresident Spouse of a U.S. Servicemember. How you present that distinction is up to you, and it interacts with the mode you’ve chosen. Guided Mode narrows the set through targeted questions; Choose Mode presents the forms and lets the employee decide. See Form modes.

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Two ways to ask

SPF exposes determination through two paths, and which one you use depends on the experience you’re building. The important thing to understand about guided flows is that their questions are a different kind of question from the ones inside a form. Flow questions decide which forms you need. Form questions fill a form out. See Question sets and navigation for how the two relate.

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