September 15, 2026: Third-Quarter Estimated Tax Payments for Partnerships, LLCs, and S Corporations

September 15, 2026, is an important tax deadline for many pass-through businesses. Partnerships and limited liability companies taxed as partnerships generally use Form 1065, while S corporations file Form 1120-S. Although these returns are typically filed after the end of the tax year, the September deadline may require owners to make their third-quarter estimated tax payment for 2026.

Who should pay by September 15?

Partnerships and S corporations usually do not pay federal income tax at the entity level. Instead, income, deductions, credits, and other tax items pass through to the partners or shareholders. Individuals who expect to owe tax on that income may need to make an estimated payment by September 15. The payment generally covers income earned during the third quarter, which includes June, July, and August.

This deadline can also matter for owners who receive income from multiple sources, including business profits, investment income, rental income, or self-employment earnings. If withholding from wages or other sources is not enough to cover the expected tax liability, an estimated payment may help reduce the risk of an underpayment penalty.

Form 1065: Partnerships and LLCs

A partnership or an LLC taxed as a partnership generally reports its activity on Form 1065 and provides each owner with a Schedule K-1. The K-1 information helps each partner estimate their share of taxable income and determine whether an additional payment is needed. Because partnership income can change during the year, owners should review updated books, distributions, and projected profits before calculating the payment.

Form 1120-S: S corporations

S corporation shareholders receive pass-through income reported on Schedule K-1. Shareholders who also work for the company should consider both reasonable compensation and pass-through income when reviewing their tax position. Payroll withholding may cover part of the obligation, but it may not cover the full amount generated by the shareholder's business income.

Steps to take now

• Update year-to-date income, expenses, payroll, and owner distributions.

• Review the latest Schedule K-1 projections from the partnership or S corporation.

• Compare expected 2026 tax with withholding and prior estimated payments.

• Submit the payment by September 15, 2026, using an approved IRS payment option.

• Keep confirmation records and revisit the estimate before the next quarterly deadline.

  
  

Tax situations vary, and state estimated-tax rules may have different dates or payment requirements. Business owners should work with their tax professional to calculate the correct amount and confirm which federal and state obligations apply. Planning before September 15 can make the payment easier to manage and help avoid unpleasant surprises when the 2026 tax return is prepared. For more information, contact The Center for Financial, Legal, and Tax Planning, P.C. at (618) 997-3436.