Payroll

Payroll Taxes & Remittances, Explained

How the Fintra payroll tax engine computes federal withholding, FICA, FUTA and SUTA, why it fails closed on unverified rates, and how remittances get paid.

Updated 11 min read1 labAccountantOwner / Founder

Payroll taxes are where "roughly right" is wrong. Fintra’s engine is deterministic - integer cents, versioned rate tables with sources and verification flags, and a stored calculation trace on every paycheck - so that any withholding amount can be justified line by line months later. This page explains what gets computed, from which rules, and what happens to the money after approval.

What the engine computes

TaxWho paysRate & basis (2025)Notes
Federal income taxEmployee (withheld)IRS Pub 15-T percentage method from W-4 electionsAnnualize wages → apply the standard or checkbox schedule → de-annualize → subtract step-3 credits → add step-4c extra
Social SecurityBoth (6.2% each)6.2% of wages up to the $176,100 wage baseYTD-aware: the cap applies exactly, even mid-check
MedicareBoth (1.45% each)1.45% of all wagesNo cap
Additional MedicareEmployee only0.9% of wages over $200,000 YTDStraddle-exact: only the portion over the threshold is taxed
FUTAEmployer only0.6% of first $7,000 per employeeAssumes the full state credit (no credit-reduction handling)
SUTAEmployer onlyYour state’s rate from your agency notice, org-configuredRate and wage base vary by state and by employer
State/local income taxEmployee (withheld)Per state table - only where verified or explicitly acceptedSee the fail-closed section below
The taxes on (and around) a 2025 paycheck

Pre-tax deductions change the bases before these rates apply: a 401(k) percentage reduces federal (and state) taxable wages but not Social Security/Medicare wages; Section 125 amounts reduce all of them; post-tax deductions reduce none. The engine applies this taxability matrix per deduction, with per-deduction overrides when a plan is unusual.

Verified rates and the fail-closed rule

All rates live in versioned database tables carrying the rate year, effective dates, source, and a verified flag. Federal 2025 tables (income tax schedules, FICA parameters, FUTA) are verified. Some state and city seeds ship unverified - and the engine will not calculate from unverified data.

  • Fail-closed means: missing or unverified rate data produces an explicit error (a 422 naming the gap) - never a silent fallback or a stale-year guess.
  • An org admin can explicitly accept specific unverified state seeds - a deliberate, recorded decision, not a default.
  • States with no income tax (e.g., TX, WA) are verified as zero-withholding.
  • A rates refresh re-seeds tables and logs the refresh - rates never change silently between runs.

Remittances: from liability to paid agency

Approving a run creates remittance liabilities - the amounts you now owe the IRS, your state, and benefit providers. The remittances view rolls these up per agency with links to the agency portals where payment actually happens.

The remittance rhythm

  1. 1

    After each approved run

    Withheld income tax + both halves of FICA accumulate toward your federal deposit; state withholding and SUTA accumulate per state; deduction amounts accumulate toward benefit providers.

  2. 2

    On your deposit schedule

    Pay federal deposits through EFTPS (monthly or semiweekly depositor - your IRS notice says which) and state amounts through the state portals. The remittance rollup tells you the amount; the agency link takes you to the payment.

  3. 3

    Record and reconcile

    Mark the remittance paid; the payment clears the liability account the GL export created, and the bank feed shows the outflow for reconciliation.

  4. 4

    At filing time

    The tax-liability, tax-payments, W-2 summary (boxes 1–6, 12D/DD, 16–17), Form 940 data, and 941-oriented reports give you (or your CPA) the numbers for the actual filings.

Reports and year-end data

  • 26 reports ship implemented, QuickBooks-style: payroll summary, details, tax liability and payments, W-2 summary, Form 940, payroll journal, cash requirements, labor cost by department, contractor payments, 1099-NEC summary, and employee-facing paystub/YTD views. Each supports CSV export.
  • A handful of specialty reports (workers-compensation, multiple-worksites, EFW2 electronic file rendering) are stubbed and clearly report themselves as not implemented rather than returning wrong data.
  • W-2 and 941/940 outputs are data reports for you or your CPA to file from - the module prepares the numbers; filing is yours.

Hands-on labs

Practice against a realistic scenario. Each lab lists the steps, what you should see, and the checkpoints that confirm you got the same result.

Lab 1

Trace one paycheck to the cent

Scenario

Priya wants to verify the engine before trusting it - auditor style. Target: Ben Carter, salary $52,000 biweekly ($2,000 gross), single, no W-4 extras, 6% 401(k), first check of the year, in a no-income-tax state.

Steps

  1. 1

    Run a draft including Ben and open his paycheck’s calculation trace.

    Expected: The trace lists each tax with base, rate, rate year, YTD before, and caps.

  2. 2

    Verify Social Security by hand: 6.2% × $2,000.

    Expected: $124.00 - the 401(k) does not reduce the SS base.

  3. 3

    Verify Medicare: 1.45% × $2,000.

    Expected: $29.00, no cap, no Additional Medicare (YTD far below $200,000).

  4. 4

    Check the federal withholding base: $2,000 − $120 (401(k)) = $1,880, annualized to $48,880 through the 2025 single schedule.

    Expected: The trace shows the annualize → schedule → de-annualize path; the withheld amount matches the trace output exactly.

  5. 5

    Verify employer-side amounts: SS $124.00, Medicare $29.00, FUTA 0.6% × $2,000 = $12.00 (first $7,000 not yet reached).

    Expected: Employer taxes match; FUTA will stop after Ben’s YTD passes $7,000.

  6. 6

    Confirm the remittance rollup after approval includes Ben’s amounts in the federal and 401(k) buckets.

    Expected: The per-agency totals move by exactly the traced amounts.

Checkpoints - you got it right if…

  • Hand-computed SS ($124.00) and Medicare ($29.00) match the trace to the cent
  • The 401(k) reduced the federal base to $1,880 but not the FICA base
  • FUTA computed on the wage base with the $7,000 cap visible in the trace
  • Approved amounts appeared in the remittance rollup per agency

Frequently asked questions

Why does my number differ from an online paycheck calculator?

Most online calculators use the wage-bracket method or an outdated year; Fintra uses the 2025 Pub 15-T percentage method with your exact W-4 elections and pre-tax deductions. Open the calculation trace and compare step by step - the trace shows the annualized wage, schedule applied, and each adjustment.

Does Fintra file my 941, 940, and W-2s for me?

It prepares the data - W-2 summary with box values, Form 940 figures, tax liability and payment reports aligned to 941 needs - and you or your CPA file through the agency systems. Remittance payments likewise happen on the agency portals, reached via the links in the remittances view.

What is a "straddle-exact" Additional Medicare calculation?

When a single paycheck crosses the $200,000 YTD threshold, only the portion above the threshold is taxed the extra 0.9% - not the whole check. The engine splits the check at the boundary exactly, and the trace shows both slices.

Our SUTA rate changed - what do I update?

Update the SUTA rate in org tax settings with the effective date from your agency notice. Rates are versioned, so prior paychecks keep the rate that was correct when they were computed.

What does it mean that AZ’s table is "known wrong" and refused?

Some shipped state seeds derive from legacy simplified tables and are flagged unverified (Arizona’s, for instance, predates the state’s move to a flat rate). Unverified tables refuse to calculate unless an org admin explicitly accepts them - the module prefers a hard stop to a wrong withholding.

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