The assumptions should be as visible as the answer.
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.
What the state pay tools calculate
The current state tools estimate annual federal income-tax liability, annual state income-tax liability and employee payroll taxes, then show that annual result across a selected number of periods. They do not reproduce an employer's payroll run.
True federal withholding uses pay-period wages and Form W-4 information under IRS Publication 15-T. State withholding can use different forms, percentages and wage bases. Until those mechanics and official fixtures are implemented, PlainSums labels the output as an annual take-home estimate and blocks filing schedules the data cannot support.
What the estimate leaves out
- Local, city and county income or occupational taxes.
- Work-state and residence-state reciprocity or multi-state allocation.
- Tax credits, dependants, itemized deductions and most Form W-4 adjustments.
- State payroll premiums and state-specific treatment of every benefit deduction.
- 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
- Internal Revenue Service: 2026 inflation adjustments and income-tax brackets
Federal annual-liability brackets and standard deductions.
- Internal Revenue Service: Publication 15-T (2026)
The payroll-withholding method PlainSums does not yet implement.
- Social Security Administration: 2026 contribution and benefit base
Social Security wage base and employee rate.
- Internal Revenue Service: Additional Medicare Tax
Liability thresholds and the additional 0.9% rate.
- Tax Foundation: 2026 state individual income-tax rates and brackets
Secondary compilation used as a starting reference; local taxes are excluded.
- Arizona State Legislature: Arizona Laws 2026, Chapter 140
Signed June 13, 2026; supersedes the earlier Arizona deduction snapshot.
- Plante Moran state and local tax advisor (April 2026): Supplemental budget with OBBBA conformity
Maine's 2026 IRC-conformity update; supersedes the earlier Maine deduction snapshot.
- Internal Revenue Service: 2026 401(k) and IRA contribution limits
Current employee deferral and IRA limits.
Validation and corrections
Automated tests cover core finance functions and release-specific regression cases, but do not constitute tax, payroll or financial review. The 51-jurisdiction primary-source audit is not complete; state estimates remain the largest residual data risk.
If a result looks wrong, email hello@plainsums.com with the route and a link to the original source. Include financial inputs only if you choose to. You can also read the privacy policy.