To file an IRS carryback claim, you apply a qualifying loss from a recent tax year against income you reported in an earlier, profitable year, then collect a refund of taxes you already paid on that income. You have two routes. Individuals, estates, and trusts use Form 1045, and corporations use Form 1139, for a tentative refund the IRS must process within 90 days. If that 12-month window has passed, or you expect the IRS to push back on the loss, you file an amended return instead: Form 1040-X for individuals, Form 1120-X for corporations. Which route fits depends on how quickly you need the money and how much time has elapsed since the loss year closed.
Confirm Your Loss Still Qualifies for a Carryback
Most net operating losses no longer qualify. For tax years beginning after December 31, 2020, the general rule under IRC Section 172 eliminates the carryback period. Post-2020 NOLs carry forward indefinitely and can offset only up to 80% of taxable income in any future year.1Office of the Law Revision Counsel. 26 U.S. Code 172 – Net Operating Loss Deduction If you’re sitting on a general business NOL from a recent year, the carryback route is closed. Carry it forward.
A few categories still qualify:
- Farming losses: two-year carryback. A farming loss is the lesser of the NOL you’d have counting only farming income and deductions, or your total NOL. If only part of the NOL is attributable to farming, only that portion carries back.2Internal Revenue Service. Instructions for Form 172 – Net Operating Losses for Individuals, Estates, and Trusts
- Non-life insurance companies: two-year carryback, paired with a 20-year carryforward.1Office of the Law Revision Counsel. 26 U.S. Code 172 – Net Operating Loss Deduction
- Unused general business credits: one-year carryback under Section 39. If your current-year business credits exceed the Section 38 tax liability limit, the excess carries back one year first; only if it can’t be absorbed does it carry forward. The filing mechanics match an NOL carryback.3Office of the Law Revision Counsel. 26 U.S. Code 39 – Carryback and Carryforward of Unused Credits
- Disaster-specific provisions: Congress occasionally enacts temporary carryback rules for federally declared disasters. If your loss ties to a specific event, check whether special legislation covered it.
If your loss falls outside these categories, stop here. There is no carryback refund available, and your path is to deduct the loss going forward.
Pick Your Filing Route
Two routes exist and they behave very differently.
The tentative carryback claim uses Form 1045 (individuals, estates, trusts) or Form 1139 (corporations other than S corporations). The IRS must act within 90 days.4Internal Revenue Service. About Form 1139, Corporation Application for Tentative Refund The catch is the filing window: you must file within 12 months after the end of the loss year. For a calendar-year taxpayer with a 2025 NOL, that means a postmark by December 31, 2026. Miss it by a day and the tentative route closes for that loss year.5Internal Revenue Service. 2024 Instructions for Form 1045
The amended return uses Form 1040-X (individuals) or Form 1120-X (corporations). Processing takes considerably longer, but the filing deadline is more generous. Use this route when the 12-month window has passed, when you expect the IRS to challenge the loss, or when a tentative claim was denied and you need a formal refund claim on record.6Internal Revenue Service. File an Amended Return
If speed matters and you’re within 12 months, file tentative. Otherwise, amend.
Calculate the Refund
A carryback refund isn’t just the loss multiplied by the old year’s tax rate. You rebuild the prior year’s return with the loss layered in, and several figures shift along with taxable income.
Compute the NOL
The NOL is generally the excess of allowable business deductions over gross income, with adjustments to ensure only genuine business losses are counted. For individuals, non-business deductions can only offset non-business income, and capital losses are limited to capital gains. Personal exemption deductions, if any apply in the loss year, are excluded.1Office of the Law Revision Counsel. 26 U.S. Code 172 – Net Operating Loss Deduction
Apply It to the Earliest Eligible Year
Push the loss into the earliest year in the carryback period. For a two-year farming carryback from 2025, start with 2023. If the loss exceeds 2023 taxable income, the remainder rolls into 2024. The sequencing is mandatory.
Rework the Prior Year’s Tax
A lower adjusted gross income in the carryback year can increase AGI-sensitive deductions and credits, including medical expenses, charitable contribution limits, and education credits. Recalculate each of them. The difference between the newly computed liability and what you originally paid, reduced by any refunds or credits already applied, is your net overpayment.
Redo the AMT
The carryback runs separately through alternative minimum tax. Your alternative tax NOL uses AMT adjustments and preferences, and the deduction is capped at 90% of alternative minimum taxable income. A waiver of the regular-tax carryback automatically waives the AMT carryback too.7Internal Revenue Service. Instructions for Form 6251 Both components combine to produce the total refund.
File the Tentative Claim (Form 1045 or Form 1139)
Your loss year income tax return must be filed before or at the same time as Form 1045. You cannot submit the tentative claim before the underlying return. Do not put both in the same envelope.
For individual filers, attach copies of the loss year Form 1040 (pages 1 and 2) with Schedules 1 through 3, plus any of Schedules A, D, F, and J that apply. Include all Schedules K-1 from partnerships, S corporations, estates, or trusts that contributed to the carryback, and Form 6251 for the loss year and each carryback year. If you extended the loss year return, include a copy of that extension application.5Internal Revenue Service. 2024 Instructions for Form 1045
Forms 1045 and 1139 cannot be filed electronically. Mail to the IRS Service Center for your area as listed in the instructions to your income tax return. Send it certified with return receipt. The postmark date controls the 12-month deadline, and you want proof.
Once the IRS receives the claim, it has 90 days to act. The review is an administrative check on mathematical accuracy, not an audit of whether the loss is legitimate. If the figures line up, the refund or credit is issued inside the window. If the IRS finds errors, it can correct the math and pay a reduced amount, or deny the claim.
A denial of a tentative claim is not a Notice of Deficiency. You cannot take it straight to Tax Court. The remedy is to file an amended return to assert a formal refund claim, which opens the standard dispute process.
File the Amended Return (Form 1040-X or Form 1120-X)
Form 1040-X can be filed electronically through tax software.8Internal Revenue Service. Instructions for Form 1040-X – Amended U.S. Individual Income Tax Return Form 1120-X is used by corporations. Both show the original figures, the net change from the carryback, and the corrected amounts. Attach the same supporting documentation you’d include with a tentative claim.
Processing typically runs 8 to 12 weeks, and can stretch to 16 weeks.9Internal Revenue Service. Where’s My Amended Return? Carryback amendments are more complex than typical ones, so expect the longer end. There is no statutory deadline forcing the IRS to act in a set number of days.
The Outer Deadline for the Refund Claim Itself
Carryback refund claims don’t follow the standard three-year refund statute of limitations. Section 6511(d)(2) sets a longer period specifically for overpayments attributable to carrybacks.
For individuals, the deadline is the 15th day of the 40th month after the end of the loss year. For corporations, the 39th month.10eCFR. 26 CFR 301.6511(d)-2 – Overpayment of Income Tax on Account of Net Operating Loss Carrybacks A calendar-year individual with a 2025 farming loss has until April 15, 2029, to file the amended return. A calendar-year corporation with the same loss has until March 15, 2029.
The clock runs from the end of the loss year, not from when the carryback year’s return was filed. The carryback year may be four or five years old, well past the normal refund window, and this special rule keeps the claim alive.
Two deadlines sit on top of each other:
- Tentative claim (Form 1045/1139): 12 months after the end of the loss year. No exceptions.
- Amended return (Form 1040-X/1120-X): the later of three years from filing the loss year return or the extended period above.
Miss the 12-month tentative deadline and the amended return route still works. Miss both and the refund is gone.
Interest on the Refund
The IRS pays interest on carryback refunds, but the start date is specific. Interest generally accrues from the later of the filing due date of the carryback year return, the date you actually filed it, or the date you paid the tax being refunded. The IRS has a 45-day administrative window to issue the refund without owing interest. If processing takes longer, interest runs from the applicable start date through the payment date.11Internal Revenue Service. Interest
If you think the IRS shorted you on interest, file Form 843 to request additional overpayment interest. The request must be received within six years of the scheduled overpayment date.11Internal Revenue Service. Interest
The Refund Doesn’t Mean the IRS Approved the Loss
A tentative refund is processed on math alone. The IRS retains the right to audit both the loss year and the carryback years at any time before the applicable statute of limitations expires, generally three years from the date you filed the loss year return. If a later audit finds the NOL was overstated or invalid, the IRS will demand repayment of the excess, with interest and potentially accuracy-related penalties. Document the deductions that generated the NOL thoroughly before you file. Those records are the first thing an examiner will request.
Check Your State Separately
A federal carryback refund does not produce an automatic state refund. States diverge from federal NOL rules in significant ways. Some cap the deduction at a fixed dollar amount or percentage of state taxable income. Some have shorter carryforward periods than the federal indefinite carryforward. A few allow carrybacks the federal code no longer permits; others prohibit them entirely. Several have suspended NOL deductions for certain years or capped them for large taxpayers. Each state where you filed in the carryback years needs its own analysis, with its own forms and deadlines.