Form 1120‑SO – South Dakota S Corporation Information Return
Last reviewed: 2025‑10‑26
Use the Form 1120so: Form 1120‑SO – South Dakota S Corporation Information Return Tax Form Calculator Form 1120so: Form 1120‑SO – South Dakota S Corporation Information Return as a stand alone tax form calculator to quickly calculate specific amounts for your 2026 1120so state tax return. Alternatively, you can use one of our Combined Federal and State Tax Estimators to quickly calculate your salary, tax, and take-home pay.
Form 1120‑SO is used by S corporations operating in South Dakota for informational purposes. While South Dakota does not impose a corporate or personal income tax, this form helps track S corporation activity within the state and supports compliance for shareholders residing or doing business in other states.
Key features of Form 1120‑SO:
- No income tax: South Dakota imposes no personal or corporate income tax, but informational filing may still be required depending on business activity.
- Multistate relevance: S corporations with South Dakota nexus and shareholders in taxable states may need to report activity for pass-through compliance.
- Local taxes: While the state has no income tax, local jurisdictions may assess business or gross receipts taxes—this form can support related filings.
- Federal linkage: Income reported should match federal Schedule K‑1 values distributed to shareholders.
| Part I Apportionment Plan Information | ||||||||
| 1 | Type of controlled group: | |||||||
| Parent-subsidiary group | ||||||||
| Brother-sister group | ||||||||
| Combined group | ||||||||
| Life insurance companies only | ||||||||
| 2 | This corporation has been a member of this group: | |||||||
| For the entire year. | ||||||||
| From , 20, until , 20. | ||||||||
| 3 | This corporation consents and represents to: | |||||||
| Adopt an apportionment plan. All the other members of this group are adopting an apportionment plan effective for the current tax year which ends on , 20, and for all succeeding tax years. | ||||||||
| Amend the current apportionment plan. All the other members of this group are currently amending a previously adopted plan, which was in effect for the tax year ending , 20, and for all succeeding tax years. | ||||||||
| Terminate the current apportionment plan and not adopt a new plan. All the other members of this group are not adopting an apportionment plan. | ||||||||
| Terminate the current apportionment plan and adopt a new plan. All the other members of this group are adopting an apportionment plan effective for the current tax year which ends on , 20, and for all succeeding tax years. | ||||||||
| 4 | If you checked box 3c or 3d above, check the applicable box below to indicate if the termination of the current apportionment plan was: | |||||||
| Elected by the component members of the group. | ||||||||
| Required for the component members of the group. | ||||||||
| 5 | If you did not check a box on line 3 above, check the applicable box below concerning the status of the group’s apportionment plan (see instructions). | |||||||
| No apportionment plan is in effect and none is being adopted. | ||||||||
| An apportionment plan is already in effect. It was adopted for the tax year ending , 20, and for all succeeding tax years. | ||||||||
| 6 | If all the members of this group are adopting a plan or amending the current plan for a tax year after the due date (including extensions) of the tax return for this corporation, is there at least one year remaining on the statute of limitations from the date this corporation filed its amended return for such tax year for assessing any resulting deficiency? See instructions. | |||||||
| Yes. | ||||||||
| The statute of limitations for this year will expire on , 20. | ||||||||
| On , 20, this corporation entered into an agreement with the Internal Revenue Service to extend the statute of limitations for purposes of assessment until , 20. | ||||||||
| No. The members may not adopt or amend an apportionment plan. | ||||||||
| 7 | Required information and elections for component members. Check the applicable box(es) (see instructions). | |||||||
| The corporation will determine its tax liability by applying the maximum tax rate imposed by section 11 to the entire amount of its taxable income. | ||||||||
| The corporation and the other members of the group elect the FIFO method (rather than defaulting to the proportionate method) for allocating the additional taxes for the group imposed by section 11(b)(1). | ||||||||
| The corporation has a short tax year that does not include December 31. | ||||||||
| Part II Taxable Income Apportionment (See instructions) | ||||||||
| Caution: Each total in Part II, column (g) for each component member must equal taxable income from Form 1120, page 1, line 30 or the comparable line of such member’s tax return. | ||||||||
Group member’s name and employer identification number | Tax year end (Yr-Mo) | |||||||
15% | 25% | 34% | 35% | (add columns (c) through (f)) | ||||
| Part III Income Tax Apportionment (See instructions) | ||||||||
Group member’s name | ||||||||
15% | 25% | 34% | 35% | 5% | 3% | (combine lines (b) through (g)) | ||
| Part IV Other Apportionments (See instructions) | ||||||||
Group member’s name | ||||||||
Accumulated earnings credit | AMT exemption amount | Phaseout of AMT exemption amount | Penalty for failure to pay estimated tax | Other | ||||
Even in no-tax states like South Dakota, informational returns like Form 1120‑SO can be crucial for tracking corporate presence and satisfying state audit trail requirements for shareholders. Accurate record-keeping of state business activities, employee count, and receipts is advised.
Last reviewed: 2025‑10‑26: If you believe this form requires an update, please contact us.
If your S corporation only has a nominal presence in South Dakota, you may still need to file Form 1120‑SO to declare this. Consult a multistate tax professional if shareholders live in taxing jurisdictions or if your corporation has operations in multiple states, as this can affect reporting obligations.
Frequently Asked Questions
Can I estimate the General Business Credit?
Start with Form 3800 and then reflect the credit here.
How much would a 401(k) contribution change my net?
Model it with the 401(k) Calculator then rerun this page with your pre-tax amount.
Considering an IRS Offer in Compromise?
Read through Form 656-B to understand eligibility and steps.
What does FICA include?
FICA includes Social Security and Medicare payroll taxes withheld from employee wages.
Important Notes
All calculations are estimates for guidance only. Always review your return and consider professional advice when submitting official filings.