W-4 Year-End Withholding Checker 2026

Annual projection and published 2026 tax parameters. Wages and income-tax withholding each equal year-to-date amounts plus remaining pay periods × the corresponding per-pay amount. Other ordinary income is added once for the full year. Projected AGI is the MAGI proxy for the child-credit phaseout. Taxable income = max(0, AGI − max(allowed itemized deductions entered, base standard deduction)). Rev. Proc. 2025-32 §4.14 gives base standard deductions of $16,100 Single/MFS, $32,200 MFJ and $24,150 Head of household; §4.01 Tables 1–4 supplies the ordinary tax brackets, including the HoH 24% bracket top of $201,750. The existing bracket engine is reused. No unpublished future-year figures are used.

Child credit and nonrefundable credits. IRC §24(a), (b), (h), as amended by Pub. L. 119-21 §70104 and Rev. Proc. 2025-32 §4.05 supply the $2,200 credit per qualifying child for 2026. Section 24(b)(1) reduces the credit “by $50 for each $1,000 (or fraction thereof)” above $400,000 MFJ / $200,000 other filing statuses: this is a ceiling-step calculation, not a continuous 5% reduction. The reduction cannot exceed the modeled child-credit base. Children are assumed under 17 and otherwise eligible, including dependency, residency and child/parent SSN requirements. Other entered credits are assumed eligible and nonrefundable. Tax = max(0, ordinary bracket tax − remaining CTC − other credits). The published ACTC refundable cap is $1,700, but ACTC earned-income refundability is not modeled; no refundable-credit balance is added.

Required annual payment: compare dollar amounts. IRC §6654(d)(1)(B) defines the lesser of 90% of current-year tax and 100% of prior-year tax. It states: “Clause (ii) shall not apply if the preceding taxable year was not a taxable year of 12 months or if the individual did not file a return for such preceding taxable year.” The optional prior-year limb is therefore available only with an amount and both confirmations. Otherwise the report names the 90% fallback. Section 6654(d)(1)(C) substitutes 110% when prior-year AGI exceeds $150,000; for MFS, clause (ii) says “clause (i) shall be applied by substituting ‘$75,000’ for ‘$150,000’.” Equality remains at 100%. Required annual payment = min(90% × projected 2026 tax, eligible 100%/110% × 2025 tax). Ties name the 90% limb. Prior-year tax means the tax determined under the Form 2210 instructions, not the balance paid when filing.

Three penalty states, separate from payment arithmetic. Section 6654(e)(1) says “No addition to tax shall be imposed” when the relevant tax “reduced by the credit allowable under section 31, is less than $1,000.” In this limited model a positive balance below $1,000 is DE MINIMIS; its additional withholding suggestion is optional, and the safe-harbor amount and shortfall are not zeroed. Otherwise, withholding at least equal to the required annual payment is SAFE HARBOR MET, with its binding limb named. A shortfall and balance of at least $1,000 is PENALTY EXPOSED. A refund or zero balance already meets the annual target. Section 6654(e)(2) is a separate prior-year no-tax-liability exception with a full-12-month prior year and U.S. citizenship or residency throughout that year. Entering prior tax of $0 does not assert that exception; a qualifying filed full-year $0 return can still supply a $0 prior-year payment limb.

W-4 action and remaining pay periods. Shortfall = max(0, required annual payment − projected income-tax withholding). Additional withholding = ceiling(shortfall ÷ remaining pay periods), in whole dollars. 2026 Form W-4 Step 4(c) says: “Extra withholding. Enter any additional tax you want withheld each pay period”. The result is additional to withholding already entered: add it to any existing Step 4(c) extra, rather than replacing that extra with this figure. A positive shortfall with no remaining pay periods displays no per-pay suggestion and a named reason. On a fresh visit, the remaining count is a rough evenly spaced calendar estimate from the date and selected frequency; actual pay dates and payroll lead time must be confirmed. Changing frequency preserves the count until a new estimate is requested. Reset restores the five-period C01 example. Shared links and saved values preserve an explicit remaining count.

Payroll information, not income-tax withholding. The SSA contribution and benefit base table and IRS Publication 15 (2026), Social security and Medicare taxes, specify the $184,500 Social Security wage base and 6.2% employee rate. Medicare is 1.45% without a wage cap; employer Additional Medicare withholding is 0.9% of wages above $200,000. These informational rows assume one employee, one employer and that entered federal taxable wages equal FICA-covered wages; pretax benefits, multiple jobs or household totals can invalidate that assumption. They are not added to the projected income tax. The IRS Additional Medicare Tax Q&A distinguishes the employer trigger from actual liability thresholds ($250,000 MFJ / $125,000 MFS / $200,000 other). Actual Additional Medicare reconciliation is outside this tool.

Input contract, rounding and scope. Money accepts complete numbers or properly grouped commas (1,234,567.89). Empty, invalid or malformed text such as 1,23 remains visible with an error and keeps the last valid full amount; changes apply on blur or Enter. Negative amounts clamp to $0, the cap is $10,000,000, and inputs round half-up to cents ($0.005 → $0.01). Untouched optional fields may be absent; explicit clear buttons restore absence, distinct from a real $0. Counts must be whole numbers within their shown ranges. Arithmetic retains full precision for tax, safe-harbor comparisons and the whole-dollar ceiling; money displays cents. Out of scope: Form 2210 quarterly penalty interest, state tax, quarterly estimated payments, ACTC wage-based refundability and W-4 worksheets beyond Step 4(c). Also excluded are capital-gain/qualified-dividend rates, self-employment tax, AMT, NIIT, QBI and special deductions, dependent/age/blind standard-deduction adjustments, MFS spouse-itemizing restrictions and credit eligibility calculations. Enter allowed itemized deductions after limits. Joint-return income/withholding must include both spouses consistently. This annual illustration is not a complete return or a guarantee about installment penalties. Illustration only. ESTIMATED · NOT ADVICE / ILLUSTRATION · NOT OFFICIAL.