Payments and credits on the module
| Type | Date (payments and offsets) | Amount |
|---|
Two prongs: when the claim is due and how much it can recover
IRC 6511(a) sets the filing deadline: a claim must be filed “within 3 years from the time the return was filed or 2 years from the time the tax was paid, whichever of such periods expires the later, or if no return was filed by the taxpayer, within 2 years from the time the tax was paid.” IRC 6511(b)(2) then caps the amount. If the claim was filed within the 3-year period, the refund cannot exceed “the portion of the tax paid within the period, immediately preceding the filing of the claim, equal to 3 years plus the period of any extension of time for filing the return”; otherwise it cannot exceed “the portion of the tax paid during the 2 years immediately preceding the filing of the claim.” Treas. Reg. 301.6511(a)-1 and 301.6511(b)-1 restate both rules. IRM 25.6.1.5 adds the practical gloss: “The look-back period is just a formula” that sets the maximum dollar refund before interest, and “If the taxpayer did not file their claim within 3 years of the return, the look-back period is 2 years.” The calculator computes both prongs and lists each payment as inside or outside the lookback. For the claim itself see refund suits and claims, Form 843 and, for penalties already paid, refund claims for paid penalties.
When tax is treated as paid, and a return as filed
The dates that drive the lookback are deemed dates, not transcript dates. IRC 6513(a) says that “any return filed before the last day prescribed for the filing thereof shall be considered as filed on such last day,” and an early payment is treated as made on the last day prescribed for payment, both determined without regard to extensions. Withholding is “deemed to have been paid by him on the 15th day of the fourth month following the close of his taxable year” (IRC 6513(b)(1)); estimated tax is “deemed to have been paid on the last day prescribed for filing the return under section 6012 for such taxable year (determined without regard to any extension of time for filing such return)” (6513(b)(2)); and a credit elect from the prior year is treated as a payment of estimated tax for the succeeding year (6513(d)). IRM 25.6.1.10.3.3.2.1 draws the conclusion in its example of a 2021 return filed May 15, 2025: “withholding credits and estimated tax payments are deemed to be paid on the Return Due Date (without regard to any extension of time to file),” so a delinquent original return filed more than three years (plus any extension) after the due date recovers none of them (Rev. Rul. 76-511). Later payments use the later of their actual date and the original due date, and offsets use the cycle posting date (IRM 25.6.1.5). The calculator applies each rule to the payment type you select.
Extensions, postponements and the last day
An extension lengthens only the 3-year lookback, not the 2-year one, and the IRM measures it in calendar months: for a claim filed August 25, 2025 with a six-month extension the “look-back period is 3 years and 6 months,” starting February 25, 2022. For claims filed after December 26, 2025, IRM 25.6.1.5 says “the look-back period is 3 years PLUS the full length of any valid filing extensions and, for claims filed after December 26, 2025, disaster postponement periods,” counting only postponement days that do not overlap an extension; the calculator applies that rule when you enter a postponement end date and the claim date is after December 26, 2025. The last day itself moves for weekends and District of Columbia holidays under IRC 7503, and the IRM treats a claim filed on the rolled day as filed on the unrolled last day for the lookback (Rev. Rul. 66-118: “The claim is treated as if it is filed on the last day otherwise prescribed for filing”). IRC 7502 makes the postmark the filing date for a mailed claim, and IRM 25.6.1.10.3.3.1.4 confirms that “A claim filed on a delinquent original income tax return that is postmarked on the last day of the three-year period, is deemed to be filed on the postmark date.”
Financial disability, and nothing else
In United States v. Brockamp, 519 U.S. 347 (1997), the Supreme Court held that “Congress did not intend the equitable tolling doctrine to apply to §6511’s time (and related amount) limitations for filing tax refund claims.” Congress responded with IRC 6511(h), which suspends the periods in 6511(a), (b) and (c) while an individual is “unable to manage his financial affairs by reason of a medically determinable physical or mental impairment of the individual which can be expected to result in death or which has lasted or can be expected to last for a continuous period of not less than 12 months,” but not “during any period that such individual's spouse or any other person is authorized to act on behalf of such individual in financial matters.” Rev. Proc. 99-21 lists what must accompany the claim: “a written statement by a physician” naming the impairment, giving the opinion that it prevented the taxpayer from managing financial affairs and met the duration test, and stating “the specific time period during which the taxpayer was prevented by such physical or mental impairment from managing the taxpayer's financial affairs,” with a signed certification; plus a statement that no person was authorized to act for the taxpayer during that period. The calculator suspends both the 3-year filing period and the lookback for the periods you enter; it cannot judge whether the statements will be accepted.
Worked example
A 2021 Form 1040 due April 15, 2022 was extended to October 15, 2022 and filed as a delinquent return claiming a refund on May 15, 2025, with $6,200 of withholding, a $2,000 estimated tax payment made September 15, 2021, and a $500 payment made April 10, 2022. The return is the claim and is filed within three years of itself, so the 3-year rule applies and the lookback is 3 years plus 6 months: November 15, 2021 through May 15, 2025. The withholding and the estimated payment are deemed paid April 15, 2022, and the $500 is treated as paid April 15, 2022 under IRC 6513(a) (the later of its date and the due date), so all $8,700 is within the lookback. Without the extension the lookback would begin May 15, 2022 and the cap would be $0, the result the IRM reaches in its own example. The calculator also reproduces the IRM's other examples: a 2024 return postmarked April 14, 2025 is treated as filed April 15, 2025 and a claim on Tuesday, April 18, 2028 is timely because April 15, 2028 is a Saturday and April 17 is the observed Emancipation Day holiday; a 2022 return filed April 14, 2023 supports a claim through April 15, 2026 but not April 16; and a claim filed May 17, 2024 on a return filed April 15, 2021 falls outside the 3-year rule and looks back two years, to May 17, 2022.
Questions practitioners ask
The client never filed the 2022 return and had withholding. How long do they have?
The original return is the claim. Withholding is deemed paid on the original due date, so a return filed within 3 years of that date (plus any extension actually granted) recovers it; after that the 2-year lookback reaches only later payments. The calculator shows the last day when you choose no return filed.
Does an extension help if the return was filed late anyway?
Yes, for the lookback. IRC 6511(b)(2)(A) adds the period of any extension to the 3 years, so a return filed within 3 years and 6 months of the April 15 due date still reaches withholding deemed paid on April 15.
The claim was mailed on the last day but received a week later. Is it timely?
Yes if it was properly addressed with postage prepaid and bears a timely postmark: IRC 7502(a) treats the postmark date as the filing date, and IRM 25.6.1.10.3.3.1.4 applies the rule to a delinquent original return that is itself the claim.
Can we argue the client was too ill to file in time?
Only through IRC 6511(h). Brockamp forecloses equitable tolling, so the claim must attach the physician statement and the no-authorized-person statement in Rev. Proc. 99-21 and show that no spouse or other person was authorized to act in financial matters during the period.
The IRS disallowed the claim and we are still talking to Appeals. Is the suit clock running?
Yes. IRC 6532(a)(1) gives 2 years from the certified or registered mailing of the notice of disallowance, and 6532(a)(4) says reconsideration does not extend it. Only a written agreement on Form 907 signed before the period ends does.