To calculate Section 1446 estimated tax on Form 8804-W, a partnership projects its effectively connected taxable income (ECTI) for the year, separates the portion allocable to corporate foreign partners from the portion allocable to non-corporate foreign partners, applies 21 percent to the corporate share and 37 percent to the non-corporate share, and divides the resulting annual tax into four quarterly installments using either equal payments or an income-based method the worksheet supports. The worksheet stays in the partnership’s records; the numbers it produces are paid to the Treasury each quarter with Form 8813.
What You Need Before You Open the Worksheet
Three things drive the whole calculation, and gathering them first prevents rework later.
Classify every foreign partner as either corporate or non-corporate. The withholding rate is 37 percent for non-corporate foreign partners and 21 percent for corporate foreign partners.1Internal Revenue Service. Partnership Withholding Foreign partners include nonresident alien individuals, foreign corporations, foreign partnerships, and foreign estates or trusts. The partnership is the withholding agent and carries the liability even if a partner never discloses foreign status.
Project total ECTI for the full tax year. ECTI is profit tied to a U.S. trade or business, and the obligation exists whether or not cash is actually distributed to the foreign partners.2Office of the Law Revision Counsel. 26 U.S. Code 1446 – Withholding of Tax on Foreign Partners Share of Effectively Connected Income Current financial statements and prior-year performance are the usual starting points.
Collect any Form 8804-C certificates. A foreign partner with deductions or losses that reduce their share of ECTI can submit Form 8804-C, letting the partnership account for those partner-level items and lower the withholding.3Internal Revenue Service. Instructions for Form 8804-C The partnership can also count 90 percent of any state and local income taxes it withholds and remits on the partner’s behalf.4eCFR. 26 CFR 1.1446-6 – Special Rules to Reduce a Partnerships 1446 Tax If a partner later fails to provide a required update, the certificate is disregarded entirely and the withholding is recalculated as if it never existed.
Running the Core Calculation
With those inputs in hand, Form 8804-W walks through the arithmetic. Enter the projected ECTI. Split it into the portion allocable to corporate foreign partners and the portion allocable to non-corporate foreign partners. Multiply the corporate share by 21 percent and the non-corporate share by 37 percent. The sum is the projected annual Section 1446 tax.
Apply any reductions from Form 8804-C certificates and the allowable state and local tax credit before dividing the annual figure into quarterly installments. Overpayments carried in from a prior period also reduce what needs to be paid in the current quarter.
Choosing an Installment Method
The worksheet offers several ways to size each of the four installments. Partnerships with uneven income should look past the default.
- Equal installments based on current-year projected tax. This is the straightforward default: annual liability divided by four.
- Prior-year safe harbor. Installments are based on the prior year’s Section 1446 tax. This is available only if the prior year was a full 12 months, the partnership timely filed its return for that year, and the prior year’s ECTI was at least 50 percent of the current year’s ECTI.
- Annualized income installment method. Each installment is calculated from income actually earned during specific periods, which helps partnerships whose income is front-loaded or back-loaded avoid overpaying early installments.
- Adjusted seasonal installment method. Available only if ECTI during any six consecutive months equals or exceeds 70 percent of total ECTI, averaged over the three preceding tax years.
When a partnership uses the annualized or adjusted seasonal method, the worksheet automatically selects the smallest required installment among all applicable methods for each payment date.5Internal Revenue Service. Instructions for Form 8804-W A partnership that begins the year on the prior-year safe harbor and later determines it will miss the 50 percent ECTI threshold can switch to the annualized income method for the remaining installments without triggering an underpayment penalty.
Hitting the Safe Harbor to Avoid Penalties
Underpayment penalties are computed separately for each installment due date, so overpaying in a later quarter does not cure a shortfall from an earlier one.6Internal Revenue Service. Instructions for Schedule A (Form 8804) – Penalty for Underpayment of Estimated Section 1446 Tax by Partnerships For any installment period, the partnership avoids the penalty if it has paid at least the smaller of the current-year tax shown on its Form 8804 (divided into equal quarterly amounts) or the prior year’s Section 1446 tax, provided the prior-year conditions above are met.
The penalty follows the principles of Section 6655, with the partnership treated as a corporation for this purpose.7eCFR. 26 CFR 1.1446-3 – Time and Manner of Calculating and Paying Over the 1446 Tax The underpayment interest rate resets quarterly. For the first quarter of 2026 it is 7 percent annualized, dropping to 6 percent for the second quarter, with large corporate underpayments at 9 percent.8Internal Revenue Service. Interest Rates Remain the Same for the First Quarter of 2026 Check the current rate before making any late payment.
Turning the Worksheet Numbers Into Payments
Each installment is remitted to the Treasury with its own Form 8813, the payment voucher that identifies the deposit as Section 1446 withholding and ties it to the partnership’s account.9Internal Revenue Service. About Form 8813, Partnership Withholding Tax Payment Voucher (Section 1446)
For calendar-year partnerships, the four installments are due April 15, June 15, September 15, and December 15. If a due date falls on a Saturday, Sunday, or legal holiday, the deadline shifts to the next business day.10Internal Revenue Service. When to File Fiscal-year partnerships use the 15th day of the 4th, 6th, 9th, and 12th months of their tax year.2Office of the Law Revision Counsel. 26 U.S. Code 1446 – Withholding of Tax on Foreign Partners Share of Effectively Connected Income Payments generally run through the Electronic Federal Tax Payment System, and EFTPS enrollment can take a couple of weeks, so register before the first installment is due.
Keep the Worksheet With the Records
Form 8804-W is not filed with the IRS. It stays in the partnership’s records as the documented logic behind each Form 8813 payment. If the IRS questions an installment amount later, the worksheet is what supports the number.
Publicly Traded Partnerships Work Differently
A publicly traded partnership does not use this installment mechanism. Withholding happens on actual distributions to foreign partners rather than on allocable ECTI, and the general installment payment rules under Section 1.1446-3 largely do not apply.11eCFR. 26 CFR 1.1446-4 – Publicly Traded Partnerships The rates are still 37 percent for non-corporate foreign partners and 21 percent for corporate foreign partners, but Form 8804-W is not the calculation tool for that regime.