Third Quarterly Tax Checklist 2025

Austin Skyline over the Colorado River towards the sunset from the Congress Street Bridge

The third quarterly tax deadline is one of the most overlooked dates of the year. Missing this deadline can mean penalties, lost cash flow, and missed planning opportunities.

That’s why we created a free Third Quarterly Tax Checklist. It’s a checklist that shows you exactly what to gather, how to calculate, and how to pay your September tax estimate.

Why You Need This Checklist

  • Stay compliant and avoid costly IRS penalties
  • Quickly confirm whether you actually need to make a payment
  • Get clarity on what income, expenses, and credits to include
  • Understand safe harbor rules so you don’t overpay or underpay
  • Streamline payment with direct IRS links and instructions

What’s Inside

Your checklist covers:

  • Eligibility check — who must pay the September quarterly estimate
  • Income and deduction review — make sure nothing is missed
  • Safe harbor thresholds — 100% vs. 110% vs. 90% rules
  • Payment options — IRS Direct Pay, EFTPS, or voucher mail-in
  • Mistakes to avoid — the most common errors that trigger penalties

Contact us to get your tax strategy in place.

You may also be interested in reading about the Third Quarter Tax Deadline.

John Roberts

John Roberts

John understands the limited resources that most small businesses possess to finance an in-house general & administrative (G&A) department, despite a critical need for a trusted partner and accounting advisor. He founded Attracct to provide relief to business owners in turning their books and financial operations over to a diligent, trustworthy CPA with a knack for small business so that owners can get their nights and weekends back and not dread the year-end close or tax prep season.