7 Mistakes You’re Making with Your June Estimated Taxes (and How to Fix Them)

NEW HAVEN, CT – Jose's Tax Service – June 11, 2026

As the second installment deadline for federal estimated taxes approaches on June 15, 2026, individuals and small business owners must ensure their financial obligations are met with precision. For the self-employed, freelancers, and families with diverse income streams, the quarterly estimated tax system serves as the primary mechanism for fulfilling tax liabilities to the Internal Revenue Service (IRS).

Failure to adhere to the stringent requirements of IRS Form 1040-ES can result in significant underpayment penalties and interest charges. At Jose's Tax Service, we observe a recurring pattern of avoidable errors during the June filing window. This technical brief outlines the seven most critical mistakes taxpayers make with their June estimated taxes and provides authoritative guidance on how to rectify them.

1. Misunderstanding the "Quarterly" Timeline!

One of the most frequent errors involves the definition of the "second quarter." While the calendar year is divided into four equal three-month periods, the IRS estimated tax schedule does not follow this logic.

• The Error: Assuming the June 15 payment covers income through June 30.
• The Reality: The second payment period for 2026 only covers income earned from April 1 through May 31.
• The Consequence: Delaying calculations until July to account for June income will result in a late payment for the April-May period.

Actionable Step: Calculate your tax liability based strictly on income received between April 1 and May 31. Ensure your payment is submitted no later than Monday, June 15, 2026.

2. Neglecting the Self-Employment Tax Component!

Self-employed individuals often focus exclusively on federal income tax brackets while overlooking the substantial impact of the Self-Employment Tax (SE tax).

• The Error: Estimating payments based only on income tax rates.
• The Technical Detail: SE tax consists of Social Security (12.4%) and Medicare (2.9%) taxes, totaling 15.3%. For 2026, the Social Security portion applies to the first $184,500 of combined wages and net self-employment earnings.
• The Fix: Use the Self-Employment Tax and Deduction Worksheet found within the 2026 Form 1040-ES instructions. Multiply your net profit by 0.9235 to determine the portion of earnings subject to SE tax before applying the 15.3% rate.

3. Ignoring the Safe Harbor Provisions!

The IRS provides "Safe Harbor" rules that protect taxpayers from underpayment penalties, even if their final tax bill is higher than anticipated.

• The Error: Guessing an amount rather than using established benchmarks.
• The Safe Harbor Rule: To avoid penalties, you should pay the smaller of:
  1. 90% of your total tax for the current year (2026).
  2. 100% of the tax shown on your 2025 return (110% if your 2025 Adjusted Gross Income (AGI) was more than $150,000, or $75,000 if married filing separately).
• The Strategy: Utilizing the prior-year safe harbor (100% or 110% of 2025 tax) is often the most secure method for those with fluctuating income.

4. Failing to Adjust for Major Life Changes!

Estimated tax requirements are dynamic. A calculation made in April may no longer be accurate by June if your personal or financial circumstances have shifted.

• The Mistake: Repeating the April payment amount without reviewing new data.
• Triggers for Adjustment:
  • Marriage or divorce, affecting filing status and tax brackets.
  • The birth or adoption of a child, which may qualify you for the Child Tax Credit (CTC).
  • Significant increases in investment income or capital gains.
  • Starting a new side hustle or business.
• The Instruction: Re-evaluate your total estimated tax for 2026 using the Estimated Tax Worksheet. If your expected tax liability has increased, you must increase your June 15 payment to remain compliant.

5. Inadequate Record Keeping and Documentation!

Sophisticated tax planning requires meticulous documentation of all income and expenses. Relying on memory or incomplete bank statements leads to inaccurate filings.

• The Command: Maintain a dedicated ledger for all business expenses and 1099 income.
• The Documentation: Retain copies of Form 1040-ES worksheets and record the confirmation numbers for all electronic payments.
• Warning: In the event of an IRS inquiry, the burden of proof rests on the taxpayer to justify the figures used in estimated tax calculations. For professional assistance with bookkeeping, visit our bookkeeping and business support page.

6. Utilizing Suboptimal Payment Methods!

How you pay is as important as how much you pay. Paper vouchers and checks are subject to mailing delays and manual processing errors.

• The Mistake: Mailing a check on June 15 and assuming it is timely.
• The Preferred Method: Use IRS Direct Pay or the Electronic Federal Tax Payment System (EFTPS). These systems provide immediate confirmation of receipt.
• Instruction: If you must mail a physical check, it must be postmarked by June 15, 2026. Use a 2026 Form 1040-ES voucher and ensure the payment is mailed to the correct IRS address for Connecticut residents.

7. Overlooking State Estimated Taxes!

While federal obligations are paramount, residents of New Haven must also consider their obligations to the Connecticut Department of Revenue Services (DRS).

• The Error: Assuming that a federal payment covers state liabilities.
• Connecticut Rule: Most Connecticut residents who expect to owe more than $1,000 in state tax (after credits) must make estimated payments using Form CT-1040ES.
• The Deadline: The Connecticut second-quarter estimated tax payment is also due on June 15, 2026.

Actionable Step: Verify your state tax liability separately from your federal estimate. Failure to pay Connecticut estimated taxes can lead to separate state-level penalties.

Practical Summary and Deadline Information

To ensure full compliance and maximize your potential refund, follow these specific commands:

1. Verify your income for April and May immediately.
2. Calculate both federal income tax and self-employment tax.
3. Cross-reference your 2025 tax return to apply the Safe Harbor rule if applicable.
4. Submit your payment electronically by 11:59 PM on June 15, 2026.
5. Book a consultation with a professional if your situation involves complex income structures.

At Jose's Tax Service, we specialize in personalized tax planning that larger chains cannot match. Whether you are a self-employed professional in New Haven or a family looking to optimize your deductions, our team provides the expert-led guidance necessary to navigate the 2026 tax year.

Contact us today for a comprehensive tax planning session or to schedule your next appointment via our official contact page.

Final Reminder: The IRS does not grant extensions for estimated tax payments. The June 15 deadline is firm. Accurate and timely payments are the only way to ensure you stay ahead of tax law changes and avoid unnecessary financial penalties.