§6622(a) · Daily Compounded · Through 6/30/2026

Interest Factor Estimator

A quick estimator of accrued IRS underpayment interest on an additional tax assessment, calculated under §6622(a) daily compounding at §6621(a)(2) quarterly rates — with Kwong v. United States (Fed. Cl. 2025) §7508A(d) COVID-window abatement applied.

Inputs
$
The Subtitle A income tax deficiency, not penalty or interest.
The year the partnership return covered.
Activates Hurricane Helene §7508A(d) window (DR-4830-GA).
Estimated Interest Through June 30, 2026
Gross — as IRS would assess
$71,800
Factor 0.7180 × principal · No abatement applied
After Kwong COVID Abatement
$47,990
1,267-day suspension window removed per §7508A(d)
After COVID + Helene (Georgia)
N/A
Toggle "Yes" if Georgia resident
§7508A(d) Abatement Claim
$23,810
Amount potentially recoverable on Form 843
Total Balance (Tax + Gross Interest)
$171,800
What the IRS demands absent any abatement

Reference Table

FACTORS · APRIL 15 FILING DATES
Filing Date Tax Year Days Gross COVID-Abated COVID + Helene COVID Share

How this works

METHODOLOGY · CITATIONS

Daily compounding under §6622(a)

IRC §6622(a) requires daily compounding of all federal tax interest. The estimator walks the timeline day by day from April 15 through June 30, 2026 — applying the applicable §6621(a)(2) quarterly rate to a running balance. A proportional allocation would overstate the COVID-window share by 15–35%.

COVID window (universal)

January 20, 2020 – July 10, 2023. 1,267 days. Kwong v. United States, No. 23-267 (Fed. Cl. Nov. 25, 2025); Abdo v. Commissioner, 162 T.C. No. 7 (2024). The IRS Acting Chief Counsel conceded in Mayronne v. Commissioner (T.C. Dkt. 1984-24, Mar. 13, 2026) that COVID-window interest is not “interest as provided by law.”

Hurricane Helene (Georgia only)

September 24, 2024 – April 30, 2025. 219 net new days beyond the COVID window. FEMA DR-4830-GA covers all 159 Georgia counties. Combined Georgia suspension across both windows: 1,486 days.

Interest starts on April 15

Under §6601(b)(1), an extension of time to file under §6081 does not extend the last date prescribed for payment. Interest accrual begins on the original April 15 due date regardless of any filing extension to October 15.

What this estimator does not include

Failure-to-pay penalties under §6651(a)(2); penalty interest under §6601(e)(2); any §6404(g) suspension already applied to the IRS Notice of Computational Adjustment; partial payments or credits during the accrual period.

Rates & verification

§6621(a)(2) quarterly rates 2012–2026 sourced from IRS Revenue Rulings. Q2 2026 rate verified at 6% per Rev. Rul. 2026-5 (IRB 2026-8). Daily rate computed as annual ÷ 365 per IRS standard practice.

Estimator only. This calculator approximates accrued IRS interest under §6622(a) daily compounding. It is not a substitute for a day-by-day reconciliation against the IRS Notice of Computational Adjustment for an actual filing. NaturalVC is a tax controversy education and document-preparation company; it is not a law firm or licensed tax-advisory practice. Nothing on this page is legal or tax advice. For an analysis of your specific assessment, contact NaturalVC to schedule a consultation.