41ESR: Underpayment of Estimated Tax and Instructions 2025 (2025)
Idaho · Idaho Tax Commission · Used for tax years 2025
Idaho Form 41ESR determines whether a corporation underpaid its 2025 estimated tax and calculates interest on any underpayment. It includes an annualized income installment calculation and is included with Form 41 or Form 41S.
Who files this form
Corporations use Form 41ESR to determine whether they underpaid Idaho estimated tax and to calculate interest on any underpayment.
A corporation must make Idaho estimated tax payments if it is required to make federal estimated tax payments and owes Idaho income tax of $500 or more.
Estimated payments are not required if:
- The corporation was not required to file an Idaho return for the previous tax year.
- The tax is due on income reported for individual owners.
If the amount on Form 41ESR, line 3, is less than $500, do not complete the form.
When it's due
- 2025 estimated payments: Idaho installment due dates are the same as the corporation’s required federal estimated tax payment due dates. Enter those dates on line 7.
- S corporations electing ABE: Make estimated tax payments by December 31 of the tax year. For this form, that is December 31, 2025.
- Interest calculation for the 2025 tax year: On line 15, use the payment date or the 15th day of the 4th month after the tax year ends, whichever is earlier. This is the endpoint for calculating underpayment interest, not a separately stated filing deadline.
What you'll need
Have these returns and records available:
- Your business name and federal Employer Identification Number (EIN).
- Your 2025 Form 41 or Form 41S, including total tax, fuels tax, sales/use tax, tax from recapture of the qualified investment exemption (QIE), and the tax reimbursement incentive credit.
- Your 2024 corporate return showing those same tax and credit amounts.
- Records of estimated tax payments, payment dates, and any amount credited from your 2024 return to 2025 estimated tax.
- Your required federal estimated tax installment dates.
If you use the annualized income method, also have Schedule A, Part II of federal Form 2220, Idaho additions and subtractions, other taxes and credits for each period, and the apportionment factor if the corporation operates in multiple states.
How to file
Include Form 41ESR with Form 41 or Form 41S. The supplied text does not give a mailing address or e-file instructions.
- Complete Part I to check for underpayments in each payment period.
- If line 13 shows an underpayment, complete Part II to calculate interest.
- Use Part III if your estimated payments are based on annualized income.
- Enter the total interest from line 24 on Form 41, line 50, or Form 41S, line 57.
Common mistakes
- Completing the form when line 3 is below $500. The form says not to complete it in that case.
- Working across columns too soon. Complete lines 9 through 14 for one column before moving to the next.
- Applying too much to a prior underpayment. The amount on line 11 must not exceed line 9.
- Using equal installments when income is annualized. Use the amounts from line 33 on Part I, line 8.
- Leaving out extra payment calculations. Additional copies may be needed when multiple payments are applied to a prior period’s underpayment.
- Completing all columns for a short-period return. Complete only the appropriate number of columns.
Questions people ask
How much is each estimated tax installment?
Each installment is 25% of the smaller of 100% of the corporation’s 2024 income tax or 90% of its 2025 income tax. If income is annualized, use the amounts calculated in Part III instead.
Can I use the annualized income method for Idaho?
Yes. If your federal estimated payments are based on annualized income, you may use that same method for Idaho. Use Schedule A, Part II of federal Form 2220 to compute federal annualized income, then follow Part III for Idaho adjustments.
What interest rates does this form use?
The form uses 6% for days in 2025 and 6% for days in 2026. Lines 19 and 20 divide the applicable number of days by 365 and multiply by the interest rate.
How do I apply an overpayment from an earlier installment?
Enter the overpayment from line 14 of the previous column on line 10 of the next column.
Where can I get help?
Call (208) 334-7660 in the Boise area or (800) 972-7660 toll free. The hearing-impaired TDD number is (800) 377-3529. The listed contact website is tax.idaho.gov/contact.