WITHHOLDINGFIX

Calculator disclaimer & methodology

Updated October 11, 2026

Planning estimate only. Withholding Fix estimates federal income tax and a possible withholding adjustment using the information you enter. It does not guarantee that you will avoid a balance due, underpayment penalty, or interest.

Supported calculations

The current calculator supports tax years 2025 and 2026, single and married-filing-jointly households, ordinary taxable income, and basic Social Security-equivalent benefit taxability. It applies the standard deduction, age-65 standard-deduction additions, and the enhanced senior deduction with its income phaseout. Senior calculations assume eligibility, including required valid Social Security numbers, and no foreign-income modifications to adjusted gross income. The higher of entered itemized deductions and the calculated standard deduction is used.

Information you supply

Pension entries must reflect their taxable amounts; the calculator does not determine contribution recovery. Nonrefundable credits, adjustments, and other deductions use the eligible amounts you supply without determining eligibility. A supplied preparer estimate replaces the calculator’s federal tax-liability estimate, while the payment comparison continues to use your entered payments.

What is not calculated

This version does not calculate state or local income tax, self-employment tax, capital-gains or qualified-dividend preferential rates, AMT, Net Investment Income Tax, Additional Medicare Tax, refundable credits, credit eligibility, dependent-filer rules, part-year or nonresident tax rules, special lump-sum benefit treatment, or underpayment penalties. It does not support married filing separately or head of household. Unsupported circumstances can materially change the result.

How the projection works

Each income row combines income received so far with the amount per future payment multiplied by remaining payment count. The calculator totals withholding already paid, expected future withholding, and separately entered estimated payments. The difference between estimated tax and projected payments is the projected balance or refund. An optional cushion increases the target amount.

Extra withholding can use equal shares, annual-income shares, custom percentages, one selected source, or fixed extra dollars per payment. Automatic allocations round up to whole dollars per payment; fixed dollar entries retain cents. It is additional to the current withholding entered, not an instruction to replace total withholding with that amount. Other form changes may alter baseline withholding. Verify the actual next payment and recalculate after changes.

Starting from last year’s income

This option uses manually entered prior-year income plus your expected annual change. It subtracts current-year income already received and spreads the remainder evenly across the remaining payment count. Current-year tax rules are applied. Prior-year tax liability, withholding, refunds, deductions, and credits are not automatically carried forward. It does not import or fully analyze a tax return, calculate safe-harbor payments, or account for uneven payment timing. Review each current-year input.

Reviewing a completed tax year

For a completed year, enter full-year income and withholding totals. Future-payment inputs are excluded. This review cannot change withholding for that year or recreate all details of a filed return. Tax-table rounding and unsupported items may produce differences.

Railroad retirement

Railroad retirement may include both Social Security-equivalent and pension-type components. Enter them separately from current statements; do not assume all Tier I is Social Security-equivalent. This version does not calculate benefit entitlements, age-62 reclassification, tax-free pension recovery, or permitted W-4V percentage elections. It allocates extra dollars only to eligible wage or pension-type sources.

Payment timing and penalties

An annual projection does not establish that payments satisfy installment deadlines or penalty exceptions. This version does not calculate safe-harbor eligibility or penalties. A projected zero balance is not a guarantee of no penalty. Allow time for payroll or pension changes to take effect.

Sources and review

Rules were checked against official guidance on October 10, 2026. The first version has automated calculation checks, but has not received independent tax-professional certification or a comprehensive audit.

Withholding Fix is independent and is not affiliated with or endorsed by the IRS, any state tax agency, or the Railroad Retirement Board.

Report a problem

Email support@withholdingfix.com with the year, filing status, and a fictional example. Do not send identification numbers or full tax returns.