Here is the straightforward, field‑tested version. You will learn what Form 8404 does, who must file, the exact due date rule, how the interest is computed, where to mail it, and the gotchas that cause rework. I will also share a quick example with real numbers so you can check your math and move on.
If your IC‑DISC reports deferred DISC income to you on Schedule K, you file Form 8404, you pay the interest, and you file it by your own return’s original due date, not the extended date.
Key Takeaways
- Form 8404 is required for IC‑DISC shareholders when deferred DISC income appears on Schedule K of Form 1120‑IC‑DISC. The IC‑DISC itself does not file it, the shareholder does.
- You file Form 8404 separately from your return by your original, unextended due date for the tax year that ends with or includes the IC‑DISC’s year end. The form lists a Kansas City, MO address.
- The annual charge is not the general IRS underpayment rate. It is a base period T‑bill rate factor defined under section 995, and the factor is shown on that year’s Form 8404. For 2024 the factor is 0.050531976 for a 366‑day year. Late payment interest, if you miss the deadline, uses section 6621 and is compounded daily.
- The calculation compares your tax with and without the deferred DISC income, the difference is your deferred tax liability, then you multiply by the year’s base period T‑bill factor.
- Corporations, other than S corporations, may deduct the Form 8404 interest in the year paid or accrued, per the form instructions. Individuals and other filers cannot.
What Form 8404 Actually Does
Form 8404 is a short, separate filing that calculates and reports the yearly interest you owe because you have deferred tax on IC‑DISC income. The mechanics are simple. You compute your actual federal income tax. Then you compute a hypothetical tax as if you had included the deferred DISC income in the current year. The difference is your DISC‑related deferred tax liability. Multiply that by the base period T‑bill rate factor published for that filing year, and that product is the interest you owe.
The IRS maintains an “About Form 8404” page that confirms purpose, links to the current PDF, and shows whether there are any developments. As of August 27, 2025, the page reports no new updates and links to the current form. Always check this page first.
Why the rate you use matters
Many preparers mix up two different interest concepts. The Form 8404 charge itself uses the base period T‑bill factor under section 995, which the IRS publishes in the form each year. However, if you pay the Form 8404 amount late, the IRS charges separate interest under section 6621, which is compounded daily, on the unpaid Form 8404 balance. Two rates, two purposes.
Who Must File, In One Line
If the IC‑DISC reports deferred DISC income to you on Schedule K, you, as the shareholder, must file Form 8404 for your tax year that ends with or includes the IC‑DISC’s year end. This includes individuals, corporations, trusts, and estates, and it applies to former IC‑DISCs as well.
Where that trigger comes from
The trigger flows from the IC‑DISC’s Schedule K, where deferred DISC income under section 995(f)(3) is allocated to each shareholder. The shareholder then picks that up for the Form 8404 computation. If there is no deferred amount, there is no Form 8404 filing for that year.
When To File, With a clear calendar example
You file Form 8404 by the due date of your federal income tax return, excluding extensions, for your tax year that ends with or includes the IC‑DISC’s tax year end. The 2024 form even includes a calendar example. For a fiscal year corporation with a tax year ending July 31, 2025, the Form 8404 due date would be November 15, 2025. For a calendar year individual with a 2024 year, Form 8404 is due April 15, 2025.
Keep one more date in mind. The actual payment of the Form 8404 interest is generally due on the fifteenth day of the fourth month after your tax year closes, unless you are a corporation with a June 30 year end, which has a special statutory rule.
Where To File and How To Pay
You mail Form 8404 to the IRS in Kansas City, Missouri, and you do not e‑file it. The form instructs you to attach a check or money order payable to United States Treasury, label it “Form 8404, Interest Due,” and include your identification number. Do not combine this with any other tax.
If you miss the payment date, the IRS charges interest, compounded daily, at the section 6621 rate on the unpaid amount until fully paid. This is separate from the base period T‑bill factor used to compute the original charge.
Filing tip, treat Form 8404 like its own mini engagement, with a checklist, a mailing control, and a proof of payment image stored with your return workpapers. It keeps small things from becoming big problems.
The What‑How‑Wow of Form 8404
- What, Form 8404 calculates the yearly interest charge on a shareholder’s DISC‑related deferred tax liability.
- How, compute your actual tax and your hypothetical tax with deferred DISC income included, take the difference, then multiply by the base period T‑bill factor shown on the form for that year.
- Wow, the form publishes a precise factor, for 2024 it is 0.050531976 for a 366‑day year, which saves you from building a daily compounding model yourself. Late payment uses a different interest regime under section 6621.
Step‑By‑Step, Filling Out Form 8404
- Identify yourself. Check your taxpayer type and enter your SSN or EIN, the IC‑DISC’s EIN, and the tax year. This matches your federal return for the year that ends with or includes the IC‑DISC’s year end.
- Line 1, enter taxable income or loss from your federal return for that year. Estimate if the return is not filed yet, and amend the 8404 later if the estimate changes.
- Line 2, enter deferred DISC income from Schedule K, Part III, line 10 of Form 1120‑IC‑DISC.
- Line 3, make the section 995(f)(2)(B) adjustments. The instructions describe carrybacks, carryovers, and other adjustments that you do or do not include for this comparison.
- Line 5 and line 6, compute tax with and without the deferred DISC income. These are chapter 1 taxes, net of credits, with exclusions for certain recapture taxes, as defined in the instructions.
- Line 7, subtract line 6 from line 5. This is your DISC‑related deferred tax liability for the year.
- Line 8, use the year’s base period T‑bill rate factor. The 2024 factor is printed in the form and is derived from the statutory definition, compounded daily over your tax‑year day count.
- Line 9, multiply line 7 by line 8 to get the interest charge due. Prepare your check to United States Treasury and note “Form 8404, Interest Due.”
- Sign the form. If you used estimates, track a tickler to amend after filing your main return if needed.
Due date details that trip people up
- The form is due by your original due date, not the extended date. Put a calendar reminder the same day you plan to file or extend your return, then mail Form 8404.
- The payment is due when your federal income tax is due for that year, generally the fifteenth day of the fourth month after year end, with a special rule for June 30 corporate year ends.
A Worked Example You Can Mirror
Assume a calendar year C corporation with 2024 taxable income of 200,000 and 50,000 of deferred IC‑DISC income reported on Schedule K. Corporate tax rate is 21 percent.
- Line 1, 200,000
- Line 2, 50,000
- Line 3, assume zero for simplicity
- Line 4, total for the comparison, 250,000
- Line 5, tax on 250,000 at 21 percent, 52,500
- Line 6, actual tax on 200,000 at 21 percent, 42,000
- Line 7, deferred tax liability, 10,500
- Line 8, 2024 base period T‑bill rate factor, 0.050531976
- Line 9, interest charge due, 10,500 × 0.050531976 = 530.59
Mail Form 8404 with a check for 530.59 to the Kansas City address shown on the form. If you pay late, the IRS charges daily‑compounded interest at the section 6621 rate on the unpaid amount. If you are a C corporation, you may deduct the Form 8404 interest in the year paid or accrued.
Shortcut, build a small template that pulls Schedule K deferred income, auto‑computes the two tax amounts, applies the year’s printed factor, and spits out a payment memo. Review takes minutes when the model is clean.
Common Errors and Easy Wins
- Using the wrong rate. The Form 8404 computation uses the base period T‑bill factor in that year’s form, not the general quarterly IRS underpayment rate. The section 6621 rate only matters if you pay the Form 8404 amount late.
- Filing on extension. The due date is your original filing due date, not the extended date. This is the most common calendar miss.
- Skipping the Schedule K cross‑check. If Schedule K shows a deferred amount, you should see a Form 8404 in your binder. If there is no deferred amount, document that in your workpapers, then move on.
- Mailing to the wrong address or combining payments. The form lists Kansas City, MO 64999, and you must send a separate payment labeled “Form 8404, Interest Due.”
Recordkeeping and amendment hygiene
- Keep the signed Form 8404, the check image, and all computations that bridge lines 1 through 7. If you used estimates, set an amendment tickler. The instructions tell you when an amended Form 8404 is required.
- Save a PDF of the year’s blank form in your workpapers. The factor printed on the form is authoritative for that filing year and helps any reviewer confirm your math quickly.
Who Files, With Source Backing
The IRS’ IC‑DISC instructions and audit guide line up on this point. Shareholders, including individuals, corporations, trusts, and estates, must file Form 8404 if the IC‑DISC reports deferred DISC income to them. The deferred tax liability is the difference between tax computed with and without the deferred income, which is the heart of the form.
E‑Filing Status and Payments
The IRS does not offer e‑file for Form 8404. The current form instructs you to mail it and to attach a separate check or money order for the full amount. This is by design, so build a mailing control that captures the date, tracking number, and a scan of the signed form.
Quality Control Checklist You Can Paste Into Your Binder
- Confirm Schedule K shows a deferred amount.
- Reconcile line 1 taxable income to the return binder.
- Compute line 5 and line 6 taxes correctly, apply chapter 1 and credit rules per instructions.
- Verify the line 8 base period T‑bill factor matches the year’s form.
- Multiply line 7 by line 8, round per your firm policy, and prepare a separate check.
- Sign, date, and mail to Kansas City, MO 64999, store proof of mailing.
- If you used estimates, set a post‑filing review to reconcile and amend if needed.
Small process upgrades that save hours
- Preload the year’s factor in your workpaper template, then lock it.
- Tie the Form 8404 mail‑date to your return e‑file day, so both move in sync.
- Add a red “8404 due” banner on the client cover sheet if Schedule K shows a deferred amount.
- Use a final reviewer step that reads only lines 5 through 9 and the check copy. If those reconcile, you are done.
A quick FAQ library
Who must file Form 8404?
IC‑DISC shareholders who are allocated deferred DISC income on Schedule K must file Form 8404 for the tax year that ends with or includes the IC‑DISC year end.
When is Form 8404 due?
By your original federal return due date, not the extended date. The 2024 form includes an example due date of November 15, 2025 for a fiscal year filer with a July 31, 2025 year end.
How is the interest computed?
Compute tax with and without deferred DISC income, take the difference, then multiply by the base period T‑bill rate factor printed in that year’s form. For 2024, the factor is 0.050531976 for a 366‑day year.
Can I e‑file Form 8404?
No. The form is mailed to the Kansas City, MO address listed in the form and paid by separate check or money order.
Is the interest deductible?
C corporations may deduct the 8404 interest in the year paid or accrued. For other filers, it is not deductible.
What if I pay late?
The IRS charges interest, compounded daily, at the section 6621 rate on the unpaid Form 8404 amount until paid. This is separate from the base period T‑bill factor used in the original computation.
Related Topics You Will Get Asked About
IC‑DISC vs FDII, a quick framing
FDII is a C corporation concept that can reduce the effective rate on eligible foreign‑derived income. IC‑DISC is an entity‑and‑shareholder structure that can convert a slice of export profit into a dividend and create a deferral that carries an annual interest charge. If you model export margins, ownership, and state rules, both can be part of the conversation, but Form 8404 applies only to the IC‑DISC interest charge on deferral. When in doubt, document assumptions and run side‑by‑side tax cash flows before you change course.
State issues and binder notes
States vary in how they treat IC‑DISC benefits. Keep a one‑page memo that lists whether your client’s filing states follow federal treatment or adjust for the economic benefit. This is not part of Form 8404, yet it belongs in the same binder so reviewers see the full picture.
A simple table you can reuse
| H4: Item | H4: Where it comes from | H4: Your entry |
| Line 1 taxable income | Your federal return for the year | __________ |
| Deferred DISC income | Schedule K, Part III, line 10 | __________ |
| Section 995(f)(2)(B) adjustments | Form 8404 instructions | __________ |
| Tax with deferral included | Line 5 result | __________ |
| Tax per return | Line 6 result | __________ |
| Deferred tax liability | Line 7 difference | __________ |
| Base period T‑bill factor | The year’s Form 8404 | __________ |
| Interest charge due | Line 9, line 7 × factor | __________ |
Process, control, and the human part
If you run a busy firm, the barrier is rarely know‑how, it is delivery. Form 8404 is tiny compared with a full return, but it can wreck a deadline if it slips through review. The fix is structure, not heroics.
- Make Form 8404 a standalone task with its own status, owner, and mail date.
- Build a tiny workpaper that requires only five numbers and the form’s printed factor.
- Close the loop with a payment image and tracking number in the binder.
Accountably helps firms that want controlled offshore capacity without losing review protection or documentation discipline. If your team needs seasonal lift to keep small filings like 8404 on track, a disciplined offshore delivery model, with SOPs, structured workpapers, layered reviews, and SLAs, can keep due dates predictable and partner time focused on client strategy. Use it where it truly solves a delivery gap, not as a band‑aid.
We build offshore delivery that lives inside your systems and templates, with multi‑layer review and clear turnaround windows, so filings like Form 8404 stop slipping through the cracks.
Final checklist and sign‑off
- You confirmed a deferred amount on Schedule K.
- You used the year’s printed base period T‑bill factor and not the quarterly IRS underpayment rate.
- You filed by your original due date, and you mailed to the address on the form with a separate payment.
- If you are a C corporation, you captured the deduction. If you are not, you documented that it is nondeductible.
- You saved proof of payment and created a tickler to amend if estimates change.
Conclusion
You do not need a long memo to get Form 8404 right. You need the right trigger, the right rate, and a clean handoff to the mail. When your team treats it as a mini engagement, your reviewers stop hunting for it, your clients stop asking about penalties, and you get your time back.
For reference, the IRS “About Form 8404” page was last reviewed on August 27, 2025, and the 2024 form currently lists the Kansas City mailing address, the year’s base period T‑bill factor, the original due date rule, and the late payment interest standard under section 6621. Check the IRS page each season for any change.
Transparency note, our team prepared this guide and verified details against current IRS sources on November 19, 2025. If you want a quick second set of eyes on your Form 8404 workflow, we can help you structure the workpaper, tie it to Schedule K, and keep it out of the fire drill pile.