K-1s arrive late. That's normal. Here's how to file Form 4868 correctly, estimate your tax payment, and file once all your K-1 data is in hand.
By Lucas Andersen — Last updated April 9, 2026
Partnerships file their own tax returns on Form 1065, due March 15 (or September 15 if the partnership itself extends). K-1s cannot be issued until the partnership’s return is substantially complete. Large midstream MLPs like EPD and ET operate across dozens of states, hold interests in subsidiary partnerships, and must reconcile complex allocation waterfalls before finalizing K-1 data. EPD typically issues K-1s in early March. ET’s 3-entity package (ET, USAC, SUN) often arrives mid-March. Some smaller or more complex partnerships issue K-1s in April or later. See 2026 K-1 release dates by ticker for typical arrival windows.
Even “on time” K-1s leave less than a month before the April 15 individual filing deadline — insufficient time for many investors to process multiple K-1s, calculate basis adjustments, and handle state filing obligations. Filing an extension is standard practice, not an exception.
Form 4868 grants an automatic 6-month extension, moving your filing deadline to October 15. No reason or justification is required. Three ways to file:
1. Electronic filing through tax software. TurboTax, H&R Block, FreeTaxUSA, and other platforms include Form 4868 filing. Complete the extension form and transmit electronically.
2. IRS Free File. Available at irs.gov/freefile for any income level (for extension purposes). File Form 4868 directly with the IRS at no cost.
3. IRS Direct Pay. Make a payment at irs.gov/directpay and select “Extension” as the payment reason. The payment itself serves as your extension — no separate Form 4868 is needed. This is the simplest method if you owe tax.
Critical distinction: Form 4868 extends the time to file, not the time to pay. Any tax owed is still due by April 15. Underpayment penalties accrue on the gap between what you owe and what you paid by that date.
IRC §6654 imposes underpayment penalties when you owe more than $1,000 at filing and haven’t made sufficient estimated payments. The safe harbor eliminates these penalties entirely:
If AGI ≤ $150,000 (prior year): Pay at least 100% of your prior-year total tax liability by April 15. Even if you owe significantly more this year, no underpayment penalty applies.
If AGI > $150,000 (prior year): Pay at least 110% of your prior-year total tax liability by April 15. The higher threshold accounts for the likelihood of income growth.
Where to find your prior-year total tax: Form 1040 line 24 (2025 return). This is the number to multiply by 100% or 110%. Round up — overpayments are refunded when you file.
| File Extension (Form 4868) | File with Estimates, Amend Later | |
|---|---|---|
| Cost | $0 (free to file) | $0 to file, but 1040-X prep costs $150–$400 if using a CPA |
| Refund timing | Delayed until you file (May–Oct) | Initial refund fast, but 1040-X takes 4–6 months to process |
| Amendment risk | None — file once with actual data | High — if estimates differ from actual K-1, 1040-X required |
| Penalty risk | None if safe harbor payment made | None if original return overpaid; interest if underpaid |
| Accuracy | Filed with actual K-1 data | Filed with estimates; accuracy depends on how close estimates were |
| Recommended for | Most MLP investors | Only if you need the refund immediately and K-1 impact is small |
For most MLP investors, the extension is the clearly superior approach. You file once, with actual data, and avoid the cost and delay of amending.
Once all K-1s are in hand, file your return using actual K-1 data. No amendment is needed because you haven’t filed yet — the extension gave you the time to wait. Most MLP investors who extend end up filing between May and August, well before the October 15 deadline.
If you sold MLP units during the year, your final-year K-1 includes the Sales Schedule needed for Form 8949. Do not file until this K-1 arrives — the §751 ordinary income allocation on the Sales Schedule determines how much of your gain is taxed at ordinary rates vs. capital gains rates.
Amended K-1s are common in partnership taxation. A partnership may discover an allocation error, receive updated information from a subsidiary, or adjust for a late audit. Amended K-1s can arrive weeks or months after the original.
If you extended and haven’t filed yet, simply use the amended K-1 in place of the original. If you’ve already filed, compare the amended K-1 to the original line by line. Assess materiality: does the change affect your federal or state tax liability? A $15 change in Box 1 on a $200 total is immaterial. A $2,000 swing in Box 1 or a new §751 amount is material and warrants Form 1040-X.