Form OW-8-ES at a glance
What it is: OW-8-ES, Oklahoma Individual Estimated Tax, Tax Year 2026 Worksheet for Individuals.
Where and when to file: A declaration of estimated tax should be filed and the first installment paid by April 15th for calendar year taxpayers.
You must make equal quarterly estimated tax payments if you can reasonably expect your tax liability to exceed your withholding by $500 or more, and you expect your withholding to be less than the smaller of: 70% of your current year's tax liability, or the tax liability shown on your return for the preceding taxable year of 12 months. (checked October 22, 2026)
Estates and farmers are not required to make estimated tax payments.
A filled-in Form OW-8-ES example: a self-employed filer's first-quarter coupon
How to fill out Form OW-8-ES, box by box
Estimated tax worksheet, lines 1 to 8
Enter on line 1 the estimated total income for tax year (less income exempt by statute).
Enter on line 2 the estimated deductions (Oklahoma standard or itemized).
Enter on line 3 the exemptions ($1,000 for each exemption). (checked October 22, 2026)
Enter on line 4 the total deductions and exemptions (add lines 2 and 3).
Enter on line 5 the estimated taxable income (subtract line 4 from line 1).
Enter on line 6 the estimated Oklahoma tax.
For part-year and nonresident taxpayers who will be filing Form 511-NR, lines 1 through 5 shall be calculated as if all income were earned in Oklahoma. Using the amount from line 5, calculate the tax; this is the base tax and will be prorated for line 6. To calculate line 6, first estimate your income from Oklahoma sources. Divide your income from Oklahoma sources by the amount on line 1. Multiply this percentage by the base tax and enter the result on line 6. This is your estimated Oklahoma tax liability. Complete the remainder of the worksheet as directed.
To compute the tax, refer to the tax table included with Packet 511 or Packet 511-NR instructions.
Enter on line 7 the estimated Oklahoma income tax credits.
Enter on line 8 the estimated Oklahoma income tax liability (subtract line 7 from 6).
Lines 9 to 12: amount to be paid with each coupon
On line 9 A, multiply line 8 by 70%.
On line B, enter the tax liability shown on your previous year's tax return.
On line 9 C, enter the smaller of line 9a or 9b.
Enter on line 10 the estimated amount of withholding.
On line 11, subtract line 10 from line 9c. If zero or less, or if line 8 minus line 10 is less than $500, stop here. You are not required to make estimated tax payments. (checked October 22, 2026)
Enter on line 12 the amount to be paid with each coupon (if paid quarterly, 1/4 of line 11).
Record of Estimated Tax Payments
The Record of Estimated Tax Payments lists Applied from 2025 Tax Return, then the Quarter, Date Paid and Amount of each payment, and the Total.
Mailing Address Change, name and Taxpayer SSN
Name and Address: Enter your name and mailing address. On a joint return, enter the name of the primary taxpayer. The primary taxpayer is the person whose name will be entered first on the income tax return.
If your address has changed, place an 'X' where indicated in the upper left corner of the coupon.
Taxpayer SSN: Enter the primary taxpayer's social security number.
Quarter, Due Date and Amount of Payment
Quarter: Enter the quarter for which you are making the estimated tax payment.
Due Date: Enter the quarterly due date. The due date for each quarter is in the Due Dates list.
Due Dates (Calendar year): 1st Quarter - April 15; 2nd Quarter - June 15; 3rd Quarter - September 15; 4th Quarter - January 15. If the due date falls on a weekend or legal holiday when the Oklahoma Tax Commission offices are closed, your payment is due the next business day.
Amount of Payment: Enter the amount of estimated tax being paid with the estimated tax coupon. Do not send coupon if no payment is required.
Please remit only one check per coupon.
Additional Information: checks, mailing and electronic payment
Make checks payable to: Oklahoma Tax Commission. Do NOT send cash.
Mail the coupon, along with payment, to: Oklahoma Tax Commission PO Box 269027 Oklahoma City, OK 73126-9027 Do not enclose any other tax reports or correspondence in this envelope.
Electronic payments are accepted for estimated income tax payments at oktap.tax.ok.gov. If you make your estimated tax payment electronically, do not mail this payment coupon. Please retain the confirmation number for your records.
There is a convenience fee charged for utilizing some of the electronic payment services.
More rules for Form OW-8-ES
Other installments for calendar year taxpayers should be paid by the due dates shown in the Due Dates (Calendar year) list.
If you receive income unevenly throughout the year (e.g. you operate your business on a seasonal basis), you may be able to lower or eliminate the amount on your required estimated tax payment for one or more periods by using the annualized income installment method. See Form OW-8-ES-SUP at tax.ok.gov.
In general, you will owe underpayment of estimated tax interest if your tax liability exceeds your withholding by $500 or more and your timely paid quarterly estimated tax payments and withholding are not at least 70% of your current year tax liability or 100% of your prior year tax liability. (checked October 22, 2026)
The tax liability is the tax due less all credits except amounts paid on withholding, estimated tax and extension payments.
The amount of underpayment of estimated tax interest is computed at a rate of 20% per annum for the period of underpayment.
No underpayment of estimated tax interest shall be imposed if the tax shown on the return is less than $1,000. (checked October 22, 2026)
After this estimated tax payment is processed, you will receive a pre-printed coupon each quarter. Please use the pre-printed coupon to make further tax payments.
Common questions about Form OW-8-ES
Is there a deadline?
A declaration of estimated tax should be filed and the first installment paid by April 15th for calendar year taxpayers.
When is this form not the right one?
Do not use this form for estimated tax payments made on behalf of the nonresident partners electing to be included in the composite return. The estimated tax payments must be made under the partnership's name and Federal Employer Identification Number using Form OW-8-ESC.
Sources
[1] Form OW-8-ES, Oklahoma Individual Estimated Tax, Tax Year 2026 Worksheet for Individuals, Oklahoma Tax Commission (the Official source link on this page).