Q4 Estimate or December Withholding? The 2026 Underpayment Penalty

Should I make a Q4 estimated payment or increase withholding to avoid the 2026 underpayment penalty?

Withholding usually wins. For a single 70-year-old with a November Roth conversion, paying nothing costs a $92 penalty, a Q4 estimate of the same shortfall leaves $57, and withholding it from a December IRA distribution leaves $0, because withholding counts as paid evenly through the whole year.

Single, 70: $40k pension (with $4,000 withheld), $30k Social Security, $60k Roth conversion in November

Couple, both 68: $60k pension (with $6,000 withheld), $50k Social Security, $120k IRA withdrawals in December

Regular method only: the annualized income installment method (Form 2210 Schedule AI), which can reduce the penalty when income arrives late in the year, is not modelled.

Why withholding wins: tax withheld counts as paid evenly through the year, whatever month it was withheld, while an estimate counts only from the day it is paid. Withholding from a December IRA distribution therefore covers the missed April, June and September installments too; a January estimate covers only the fourth. The penalty dates follow the 2026 installment calendar (2026-04-15, 2026-06-15, 2026-09-15, 2027-01-15) and the IRS underpayment rates as announced, with the unannounced quarters at the latest announced rate.

Check your Q4 estimate against the safe harbor
Free: your 2026 baseline, one move in full and your combined total.

Download the data

Every row on this page, with its inputs: q4-estimate-vs-december-withholding-2026.csv · q4-estimate-vs-december-withholding-2026.json (CC0).

Questions

What is the safe harbor for 2026?

Pay at least 90% of the 2026 tax or 100% of the 2025 tax (110% if 2025 AGI was over $150,000, $75,000 married filing separately) through withholding and timely estimates.

Does it matter that the income came late in the year?

It can. These figures use the Form 2210 regular method, which spreads the year's required payment evenly over the four installments. The annualized income installment method (Schedule AI) can lower or remove the penalty when most income arrives late in the year; it is not modelled here, so treat these penalties as the regular-method amount.

When is the fourth 2026 estimated payment due?

January 15, 2027.

Can withholding from an IRA distribution really count for the whole year?

Yes. Under the estimated-tax rules, income tax withheld is treated as paid in four equal parts on the installment dates unless you elect otherwise, whatever month it was withheld.

Sources and method

Every figure was computed by QuantCalc's open tax engines — federal 2.0.0 and state 1.12.0, the same engines behind the federal and state tax APIs — for the 2026 tax year. The engine documentation lists the official source of every rule; the rules this study leans on:

• 26 U.S. Code § 6654
• 26 U.S. Code § 6654
• Quarterly interest rates

Federal tax uses the tax rate schedule (the IRS Tax Table, used on returns below $100,000 of taxable income, differs by a few dollars). Households are illustrations, not averages. A joint household's pension, IRA withdrawals and conversion are split evenly between the spouses, so each spouse's own retirement exclusions apply; state tax comes from the state engine through its public API with exactly that split. The full inputs of every row are in the data files, and every row can be re-run through the public APIs.

An estimate, not tax advice. These are computed examples for the 2026 tax year from QuantCalc's open tax engine. Your own return depends on facts these examples do not include. Check any move with your tax preparer or account custodian before acting.

@misc{quantcalc2026payaq4estimateorwithholdfromaniraindecem,
  title  = {Pay a Q4 Estimate or Withhold From an IRA in December? The 2026 Underpayment Penalty, Computed},
  author = {{QuantCalc Research}},
  year   = {2026},
  url    = {https://quantcalc.app/research/q4-estimate-vs-december-withholding-2026/},
  note   = {Accessed <date>}
}