IT-2105.9: Underpayment of Estimated Income Tax By Individuals and Fiduciaries - for tax year 2025 (2025)
New York · NY DTF · Used for tax years 2025
Form IT-2105.9 calculates underpayments of estimated tax and any resulting penalty for individuals and fiduciaries for 2025. It covers New York State, New York City, Yonkers, and MCTMT taxes and includes short and regular methods for computing the penalty.
Who files this form
Form IT-2105.9 is for individuals and fiduciaries computing an estimated tax underpayment penalty for New York State, New York City, Yonkers, and MCTMT.
All filers using this form must complete Part 1. If line 15, current-year tax minus income taxes withheld, is less than $300, the form says not to complete the rest of the form.
The supplied form does not give complete rules for determining who must file.
When it's due
For tax year 2025, the form prints these estimated tax payment due dates:
- First installment: April 15, 2025.
- Second installment: June 15, 2025.
- Third installment: September 15, 2025.
- Fourth installment: January 15, 2026.
The 2025 penalty calculations also use April 15, 2026. Under the short method, line 23 depends on whether the underpayment was paid before that date or on or after it.
The form does not print a separate filing deadline for Form IT-2105.9.
What you'll need
Have these returns and payment details available to complete the form:
- Your 2025 New York return: Form IT-201, IT-203, or IT-205, as applicable, for tax, credits, and withholding amounts.
- Your 2024 tax amount for line 16. The form cautions you to consult the instructions for this amount.
- Your total STAR credit amount for line 7a.
- Estimated tax payment amounts and dates, including when any underpayment was paid.
- Your name as shown on your return and your identification number, either an SSN or EIN.
How to file
Submit Form IT-2105.9 with your New York State return. The supplied form does not provide a mailing address or e-file directions.
Enter the penalty from line 24, if using the short method, or line 39, if using the regular method, on the applicable return:
- Form IT-201, line 81.
- Form IT-203, line 71.
- Form IT-205, line 42.
Common mistakes
- Do not overlook the cautions on lines 1 and 16. Both tell you to consult the instructions when entering your 2025 total tax and 2024 tax. Those instructions were not supplied here.
- Do not continue past line 15 if the result is less than $300. The form explicitly tells you to stop.
- Do not forget to submit this form with your New York State return.
Questions people ask
When can I use the short method?
The form directs you to complete Part 2 if you paid withholding tax and/or four equal estimated tax installments on the due dates, or if you made no estimated tax payments. Otherwise, you must use Part 3, the regular method.
What if line 21 is zero or less?
Under the short method, the form says you do not owe the penalty if line 21 is zero or less.
Does paying before April 15, 2026, affect the short-method calculation?
Yes. For tax year 2025, line 23 multiplies the amount on line 21 by the number of days paid before April 15, 2026, and then by .00026. That result is subtracted from line 22. If the amount was paid on or after April 15, 2026, enter zero on line 23.
How do I work through the regular-method columns?
In Part 3, Schedule A, complete lines 27 through 29 one column at a time, starting with column A.