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PlainSums publishes deterministic planning tools. This page records the calculation contract, public sources and known limitations behind the current release. It does not imply independent professional approval.

Tax year
2026
Formula version
2026.10.29
Tax data version
2026.10.29-interim
Updated
2026-10-29

Which tax year these numbers are

Every rate, bracket, threshold and contribution limit on this site is the tax year 2026 figure. The federal parameters below are read directly from the code that does the arithmetic, so what you see here is what the calculators use — not a separately maintained copy that can fall out of step with them.

Federal tax parameters used by PlainSums calculators for tax year 2026
Figure2026How it is applied
Standard deduction$16,100 single / $32,200 marriedSubtracted before the federal brackets are applied.
Social Security wage base$184,500Employee rate 6.2%, charged once per year up to this amount and not at all above it.
Medicare rate1.45%Employee rate on all wages. There is no wage cap.
Additional Medicare Tax threshold$200,000 single / $250,000 married0.9% on wages above the threshold, employee only — there is no employer match. Employer withholding is triggered at $200,000 for everyone and reconciled on the return.
401(k) elective-deferral limit$24,500Standard employee limit; catch-up eligibility is not assumed.

State schedules encode the same tax year. Where a state enacted a mid-cycle rate change for 2026, the change is reflected and noted on that state's page. Connecticut and New York do not tax high earners at their marginal rates alone — both claw back the value of their lower brackets — and those mechanisms are applied here from the state schedules listed below.

What the state pay tools calculate

The state pay tools open on a per-paycheck view. Federal income tax is withheld the way payroll software does it: the paycheck's taxable wages (after a traditional 401(k) and other pre-tax deductions) are annualized, adjusted by the Form W-4 entries you give — Step 2 checkbox, Step 3 credits, Step 4(a) other income, Step 4(b) deductions and Step 4(c) extra withholding — and run through Worksheet 1A and the 2026 annual percentage-method tables in IRS Publication 15-T. With no W-4 adjustments, a year of that withholding equals the federal tax the annual model computes, and the test suite checks that it does.

The state income-tax line is the year's estimated state tax divided by the number of paychecks. Each state publishes its own withholding formula, which can land a little higher or lower per check. Social Security, Medicare and state payroll programs are averaged across the year. The Annual tax view instead shows the year's estimated liability divided into pay periods for display. Filing schedules the data cannot support are blocked rather than approximated.

16 states require employee-paid payroll programs — disability insurance, paid family and medical leave, WA Cares, Alaska and New Jersey unemployment insurance, Pennsylvania unemployment compensation, Oregon's statewide transit tax and Vermont's child care contribution. Each is deducted from gross wages at its 2026 employee rate and wage cap, as published by the state agency listed under sources. Where the law lets an employer pay part of the employee share, the calculator deducts the most the employer may charge. Maryland's Family and Medical Leave Insurance (FAMLI) starts with wages paid on January 1, 2027, so it is not in the 2026 estimates; the Maryland FAMLI calculator works it out by pay date.

Salaried state calculators can add local income tax when you select a listed or custom rate. This is a flat-rate planning estimate using the documented tax base, and the listed rates are representative. Confirm the applicable rate with your locality. Hourly estimates and comparison tables exclude local income tax.

What the estimate leaves out

  • Local, city and county income or occupational taxes unless you select a rate in a salaried state calculator. Progressive local brackets, credits and jurisdiction-specific rules are not modeled.
  • Work-state and residence-state reciprocity or multi-state allocation.
  • Tax credits and itemized deductions in the annual tax view. (The per-paycheck view uses your Form W-4 Step 3 and Step 4 entries for federal withholding.)
  • Income-based phase-outs of a state standard deduction or personal exemption. Every state deduction here is a fixed amount; where a state shrinks it as income rises (Connecticut, Maine, Maryland, Rhode Island, Utah and Wisconsin), that state's page says so.
  • Married filing separately, which no state schedule in this data set covers.
  • State-specific treatment of every benefit deduction, per-hour charges such as Oregon's Workers' Benefit Fund assessment, and employer-specific choices to pay part of an employee's paid-leave premium.
  • Year-to-date pay, prior withholding, bonuses and employer payroll rounding.

General calculator formulas

Loan tools use standard fixed-rate amortization. Saving and investing tools use compound-growth and annuity formulas with the timing shown beside each input. Scenario returns are steady mathematical assumptions, not forecasts or probabilities. Result statements show the components used by the calculation; anything not represented by an input should be treated as excluded.

Source register

Validation and corrections

Automated tests cover core finance functions and release-specific regression cases, but do not constitute tax, payroll or financial review. Every one of the 51 jurisdictions is pinned to a hand-computed expected figure. Bracket boundaries, rates and deduction amounts have been checked against the 2026 schedules in the source register below, and Connecticut and New York additionally against their own state publications.

Two known gaps remain. Maine's standard deduction is disputed between published 2026 sources, so its figure is the least certain in the data set. And a secondary compilation, however carefully cross-checked, is not the statute — a state that changes its schedule after this release will be wrong here until it is updated. State estimates remain the largest residual data risk.

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