This tool does not provide financial, investment, tax, legal, or accounting advice, and using it does not create any advisory or professional relationship. It is a self-service calculator for general educational and informational purposes only. Nothing it displays should be taken as a recommendation to choose any contribution election, W-4 setting, or other action. This tool also sells nothing — it runs no ads and has no affiliate, referral, or sponsorship relationships with any brokerage, bank, payroll company, advisor network, or financial company, so it earns nothing from what you decide and has no incentive to steer you toward any product or provider.
Federal withholding here is computed with the IRS 2026 Pub 15-T percentage method (the automated-payroll formula, for 2020-or-later W-4s) — the same structure your payroll system uses. But withholding is a prepayment estimate: your actual April refund or balance due depends on your full year and complete return. Amounts are also spread evenly across the year, while real paychecks change mid-year when the Social Security wage base ($184,500) or the Additional Medicare threshold ($200,000) is crossed, or when you change your W-4 or contributions.
The calculator models 2026 federal withholding, Social Security and Medicare (including the wage base and Additional Medicare withholding), all-51-state income taxes (brackets, standard deductions, and exemptions applied annually pro-rata), the larger employee payroll programs (such as CA SDI, WA PFML/WA Cares, NJ UI/TDI/FLI, and paid-leave premiums in a dozen more states), a user-entered local income tax rate, and the pre-tax treatment of Traditional 401(k), HSA, and §125 premiums — including Pennsylvania's and California's/New Jersey's exceptions. Real payrolls have more moving parts: bonuses and supplemental wages, employer benefit quirks, imputed income, multi-state work, wage garnishments, mid-year changes, credits and phase-outs not modeled here, and more. Some state details are deliberately simplified (noted in the tool): a few personal-credit and deduction phase-outs, Alabama's and Missouri's federal-tax deductions, Oregon's federal subtraction, local taxes beyond a single flat rate, and Ohio school-district surtaxes.
The comparison assumes the same contribution invested either way, a constant growth rate you choose, and a single retirement tax rate you choose. Real outcomes depend on future tax law, your future income, state of retirement, RMD rules, employer match mechanics, and decades of market returns — all unknowable. It is a framework for thinking, not a prediction.
Every figure is a projection built from the inputs you provide using simplified math. Tax rules change — sometimes retroactively (five states changed their 2026 rates in spring 2026 alone, after most published tables were printed). Actual results will differ. No accuracy, completeness, or outcome is promised, and the calculations may contain errors. Do not make financial decisions based on this tool alone.
State withholding is estimated by applying each state's 2026 annual brackets, standard deduction, and exemptions pro-rata — structurally similar to most states' own withholding formulas, but not identical to any particular employer's implementation. Rates and thresholds were gathered from state revenue department and legislative sources in July 2026. Always confirm with your state's tax authority or a professional before relying on a specific number.
For a decision as long-lived as a Roth election, a fee-only fiduciary advisor or CPA who is paid for advice rather than for selling a product is worth real money.
This is an independent, privately made tool. It is not created, endorsed, sponsored, or reviewed by any government agency, employer, payroll processor, brokerage, or financial company.
This tool is provided "as is," without warranty of any kind, express or implied, including any warranty of accuracy, merchantability, or fitness for a particular purpose. To the fullest extent permitted by law, the author shall not be liable for any loss or damages of any kind arising from your use of, or reliance on, this tool or its output. Your use is entirely at your own risk.
This tool is free to use. If a "tip" or "support" option is offered, any payment is a voluntary gift, is not a purchase of the tool or of any service, is not required to use any feature, and is non-refundable. Supporting the project does not entitle you to advice, support, or any particular result, and does not change any part of this disclaimer.
The tool and this notice may be updated at any time; the "Last updated" date above reflects the latest revision. Continued use means you accept the current version.
© 2026 Marcus Cunningham. All rights reserved. This tool is free to use, and you're welcome to share the link — but its code is not licensed for reuse, redistribution, rehosting, or repackaging. Please point people to the official site rather than copying the page.