September 2023 Individual Due Dates

September 1 – 2023 Fall and 2024

Tax Planning Contact this office to schedule a consultation appointment.

September 11 – Report Tips to Employer

If you are an employee who works for tips and received more than $20 in tips during August, you are required to report them to your employer on IRS Form 4070 no later than September 11. Your employer is required to withhold FICA taxes and income tax withholding for these tips from your regular wages. If your regular wages are insufficient to cover the FICA and tax withholding, the employer will report the amount of the uncollected withholding in box 8 of your W-2 for the year. You will be required to pay the uncollected withholding when your return for the year is filed.

September 15 – Estimated Tax Payment Due

The third installment of 2023 individual estimated taxes is due. Our tax system is a “pay-as-you-earn” system. To facilitate that concept, the government has provided several means of assisting taxpayers in meeting the “pay-as-you-earn” requirement. These include:

  • Payroll withholding for employees;
  • Pension withholding for retirees; and
  • Estimated tax payments for self-employed individuals and those with other sources of income not covered by withholding.

When a taxpayer fails to prepay a safe harbor (minimum) amount, they can be subject to the underpayment penalty. This penalty is equal to the federal short-term rate plus 3 percentage points, and the penalty is computed on a quarter-by-quarter basis.

Federal tax law does provide ways to avoid the underpayment penalty. If the underpayment is less than $1,000 (the de minimis amount), no penalty is assessed. In addition, the law provides “safe harbor” prepayments. There are two safe harbors:

  • The first safe harbor is based on the tax owed in the current year. If your payments equal or exceed 90% of what is owed in the current year, you can escape a penalty.
  • The second safe harbor is based on the tax owed in the immediately preceding tax year. This safe harbor is generally 100% of the prior year’s tax liability. However, for taxpayers whose AGI exceeds $150,000 ($75,000 for married taxpayers filing separately), the prior year’s safe harbor is 110%.

Example: Suppose your tax for the year is $10,000 and your prepayments total $5,600. The result is that you owe an additional $4,400 on your tax return. To find out if you owe a penalty, see if you meet the first safe harbor exception. Since 90% of $10,000 is $9,000, your prepayments fell short of the mark. You can’t avoid the penalty under this exception.

However, in the above example, the safe harbor may still apply. Assume your prior year’s tax was $5,000. Since you prepaid $5,600, which is greater than 110% of the prior year’s tax (110% = $5,500), you qualify for this safe harbor and can escape the penalty.

This example underscores the importance of making sure your prepayments are adequate, especially if you have a large increase in income. This is common when there is a large gain from the sale of stocks, sale of property, when large bonuses are paid, when a taxpayer retires, etc. Timely payment of each required estimated tax installment is also a requirement to meet the safe harbor exception to the penalty. If you have questions regarding your safe harbor estimates, please call this office as soon as possible.

CAUTION: Some state de minimis amounts and safe harbor estimate rules are different than those for the Federal estimates. Please call this office for particular state safe harbor rules.

Weekends & Holidays:

If a due date falls on a Saturday, Sunday or legal holiday, the due date is automatically extended until the next business day that is not itself a legal holiday.

Disaster Area Extensions:

Please note that when a geographical area is designated as a disaster area, due dates will be extended. For more information whether an area has been designated a disaster area and the filing extension dates visit the following websites:

FEMA: https://www.fema.gov/disaster/declarations
IRS: https://www.irs.gov/newsroom/tax-relief-in-disaster-situations

For example, disaster-area taxpayers in most of California and parts of Alabama and Georgia now have until Oct. 16, 2023, to file various federal individual and business tax returns and make tax payments.

September 2023 Business Due Dates

September 15 – S Corporations

File a 2022 calendar year income tax return (Form 1120-S) and pay any tax due. This due date applies only if you requested an automatic 6-month extension. Provide each shareholder with a copy of their Schedule K-1 (Form 1120-S) or a substitute Schedule K-1 and, if applicable, Schedule K-3 (Form 1120-S) or substitute Schedule K-3 (Form 1120-S).

September 15 – Corporations 

Deposit the third installment of estimated income tax for 2023 for calendar year

September 15 –  Social Security, Medicare and withheld income tax

If the monthly deposit rule applies, deposit the tax for payments in August.

September 15 – Nonpayroll Withholding

If the monthly deposit rule applies, deposit the tax for payments in August.

September 15 – Partnerships

File a 2022 calendar year return (Form 1065). This due date applies only if you were given a 6-month extension. Provide each partner with a copy of their Schedule K-1 (Form 1065) or a substitute Schedule K-1 and, if applicable, Schedule K-3 (Form 1065) or substitute Schedule K-3 (Form 1065).

Weekends & Holidays:

If a due date falls on a Saturday, Sunday or legal holiday, the due date is automatically extended until the next business day that is not itself a legal holiday.

Disaster Area Extensions:

Please note that when a geographical area is designated as a disaster area, due dates will be extended. For more information whether an area has been designated a disaster area and the filing extension dates visit the following websites:

FEMA: https://www.fema.gov/disaster/declarations
IRS: https://www.irs.gov/newsroom/tax-relief-in-disaster-situations

For example, disaster-area taxpayers in most of California and parts of Alabama and Georgia now have until Oct. 16, 2023, to file various federal individual and business tax returns and make tax payments.


If you have any questions, please contact our office at (503) 224-5321. Isler Northwest LLC is a firm of business advisors and CPAs in Portland, Oregon. Our service goal at Isler Northwest is to earn our clients’ trust as their primary business and financial advisor.

Isler Northwest
(503) 224-5321
1300 SW 5th Avenue
Suite 2900
Portland, Oregon 97201