Introduction
Form 1120 is the U.S. Corporation Income Tax Return. The corporate rate on it applies to taxable income, not to revenue or accounting profit. That gap trips up plenty of Australian founders and finance teams who hold U.S. companies.
If you run a U.S. subsidiary, hold shares in a Delaware C corporation, or manage books for one, this guide covers the 2026 federal rate, how the calculation works, state taxes, cross-border issues and filing deadlines.
All amounts below are in U.S. dollars (US$) unless stated. Confirm every figure against current IRS guidance before you file.
Key Takeaways
- The federal rate is 21%, but it applies only to correctly determined taxable income.
- Form 1120, 1120-S and 1120-F serve different entity types.
- State taxes, credits, losses and foreign-owner rules change the total cost.
- Accurate books and ownership records keep filings defensible.
What Is Form 1120 and Who Must File It?
The IRS describes Form 1120 as the return domestic corporations use to report income, gains, losses, deductions and credits, and to figure federal income tax. It reports taxable income after tax adjustments. It does not tax gross sales, cash received or bottom-line book profit.
Who must file
- Domestic C corporations
- Eligible LLCs that elected corporate treatment on Form 8832 (a classification election, not a separate LLC return)
Generally, domestic corporations file whether or not they have taxable income, unless exempt or required to file a special return. A dormant U.S. subsidiary generally must still file.
Form 1120 vs 1120-S vs 1120-F
| Aspect | 1120 | 1120-S | 1120-F |
|---|---|---|---|
| Entity | Domestic C corporation | Qualifying S corporation | Foreign corporation with a U.S. trade or business |
| Tax treatment | Taxed at corporate level | Pass-through to shareholders | Taxed on U.S.-connected income |
| Ownership limits | None | Up to 100 shareholders, one class of stock, no nonresident-alien shareholders | None specific |
| Election | Default for corporations | Form 2553 | Not applicable |
The S corporation ownership limits mean most Australian-owned U.S. companies cannot use Form 1120-S, because nonresident aliens and corporations are not allowable shareholders.
Penalties for getting it wrong
Under the Form 1120 instructions, late filing generally costs 5% of unpaid tax per month, up to 25%. Late payment generally costs 0.5% per month, also capped at 25%. For returns required in 2026, the minimum late-filing penalty for a return more than 60 days late is the smaller of the tax due or $525.
What Is the 2026 Form 1120 Corporate Tax Rate and How Is It Calculated?
The US federal statutory rate is 21% of taxable income under IRC section 11(b). It has stayed flat for tax years beginning after 31 December 2017. US 2025 legislation changed tax-base rules, such as depreciation and research expensing, but not the percentage. The 21% rate still applies for 2026.
The calculation sequence
- Start with gross income
- Subtract allowable deductions and other permitted adjustments
- Arrive at taxable income
- Multiply by 21% (Schedule J, line 1a)
- Apply credits and other tax items
- Subtract estimated payments to find the balance due
Hypothetical example
Illustrative figures only.
| Item | Amount |
|---|---|
| Revenue | $2,000,000 |
| Cost of goods sold | $900,000 |
| Wages, rent and other deductions | $700,000 |
| Taxable income | $400,000 |
| Federal tax at 21% | $84,000 |
Multiplying 21% by revenue would give $420,000, five times too high. Book profit can also differ from taxable income, for example when meals are only 50% deductible or depreciation is accelerated for tax.
Book-to-tax reconciliation
Schedule M-1 reconciles financial-statement income with the income on Form 1120. Schedule M-3 generally replaces it when total assets are $10 million or more at year-end. Smaller corporations may file M-3 voluntarily.
Statutory vs effective rate
The statutory rate is the legislated 21%. An effective rate measures tax paid against some measure of income, so credits, losses and timing can pull it away from 21%. If you quote an effective rate, GAO's analysis shows why you must state the measure and denominator used.
What Can Change the Final Form 1120 Tax Liability?
Deductions and items needing review
Ordinary and necessary expenses reduce taxable income when documented: cost of goods sold, wages, rent, interest and depreciation. Some items need a closer look:
- Business meals are generally 50% deductible
- Entertainment is generally nondeductible
- Government fines and penalties are generally nondeductible
- Accruals, reserves and depreciation differences can shift deductions between years
Current rules affecting 2026
- Net operating losses: post-2017 NOLs generally offset up to 80% of taxable income and carry forward without expiry.
- Interest limit (section 163(j)): deductible interest is generally capped at business interest income plus 30% of adjusted taxable income. The small-business exemption threshold for 2026 is $32 million of average gross receipts.
- Research costs: section 174A allows current deduction of domestic research expenditure for tax years beginning after 31 December 2024. Foreign research is still amortised over 15 years.
- Depreciation: 100% bonus depreciation applies to qualified property acquired after 19 January 2025. The 2026 section 179 maximum is $2,560,000.
- Credits: general business credits go through Form 3800.
- Corporate AMT: the 15% minimum tax generally hits only corporations averaging over $1 billion in adjusted financial statement income.
In VJM Global's U.S. work, bonus depreciation often creates the biggest gap between book and tax income. It lets a business deduct a large share of an asset's cost in the year the asset is placed in service.
The two-level tax effect
A C corporation pays 21% on profits. Distributing after-tax profits as dividends can trigger a second layer. For an Australian shareholder, U.S.-source dividends generally face 30% withholding unless a treaty reduces it.
Under the U.S.-Australia treaty protocol, the limit is 5% for a company holding at least 10% of voting power, and 15% otherwise. A 0% rate can apply at 80% ownership if the limitation-on-benefits tests are met. This withholding does not reduce the corporation's own 21%.
Choosing a structure
No structure wins universally. Weigh:
- C corporation: suits outside investors and reinvested profits, with double-tax exposure on distributions
- S corporation: pass-through, but ownership rules generally exclude Australian shareholders
- Corporate-taxed LLC: flexible governance with C corporation tax treatment
State exposure, distribution plans and Australian tax treatment should drive the decision.
State and Cross-Border Issues for Australian Businesses
State taxes sit on top
Federal 21% is not the full U.S. cost. Tax Foundation's 2026 table shows 44 states levy corporate income tax, with top rates from North Carolina's 2.0% to New Jersey's 11.5%.
Other taxes work differently:
- Washington B&O tax applies to gross income with no ordinary expense deductions
- Texas franchise tax is based on taxable margin
- Ohio CAT and Nevada Commerce Tax apply to in-state gross receipts
- Delaware corporations file an annual report and pay franchise tax by 1 March
Nexus is state-specific, and apportionment (using property, payroll and sales factors) decides how much profit each state taxes. Sales-tax registration is also state-by-state.
Separate from Australian obligations
A Form 1120 filing does not replace Australian company tax, GST (10%), BAS, PAYG instalments or PAYG withholding. Australian owners may also face CFC attribution under ATO rules. That is a separate Australian analysis and does not change the U.S. rate.
A U.S.-Australia treaty permanent establishment generally needs a fixed place of business or a dependent agent. Control between companies alone does not create one.
Foreign-owned U.S. corporations
Check whether these apply:
- Form 5472: required for a 25%-foreign-owned U.S. corporation with reportable related-party transactions. The penalty is $25,000 per failure, and it increases after IRS notice.
- Disregarded entities: foreign-owned ones generally file a pro forma Form 1120 with Form 5472 attached.
- Transfer pricing: related-party dealings must meet the arm's-length standard, with documentation in place when the return is filed.
- BOI reporting and withholding: treat beneficial ownership filings and withholding on intercompany payments as separate compliance items.
Form 1120 Filing Deadlines and a 2026 Compliance Checklist
Deadlines
Form 1120 is generally due on the 15th day of the fourth month after year-end. Match each due date to the correct tax year:
- 15 April 2026 is the deadline for calendar-year 2025 returns
- A calendar-year 2026 return is due 15 April 2027
- Form 7004 gives a six-month filing extension, to 15 October for calendar-year filers
- The extension does not defer payment; tax is due at the original deadline
- June 30 year-ends are due in the third month, and short periods follow special rules
Estimated tax is required when expected tax is $500 or more. Calendar-year corporations typically pay in four instalments:
- 15 April
- 15 June
- 15 September
- 15 December
Corporations that file 10 or more returns of any type in a year generally must e-file.
Preparation checklist
Gather these records before you start the return:
- Prior-year return
- EIN and formation documents
- Trial balance and general ledger
- Income records and cost-of-goods-sold data
- Payroll records
- Fixed-asset and depreciation schedules
- Ownership information and related-party transactions
- Tax payments and state filings
- Foreign-owner records
VJM Global supports international businesses with U.S. obligations through accounting, financial reporting and tax-compliance coordination, with CPAs and Chartered Accountants working from clean books and cross-border documentation.
Frequently Asked Questions
How much tax do I pay on 1120?
It depends on taxable income, the 21% federal rate, deductions, credits, losses, state taxes and payments already made. Your specific facts decide the final figure.
Is Form 1120 the same as Form 1120-S?
No. Form 1120 is the regular C corporation return; Form 1120-S is the S corporation pass-through return. The right one depends on a valid Form 2553 election and eligibility.
Who needs to file Form 1120?
Domestic C corporations and LLCs taxed as corporations. Foreign corporations and exempt organisations may follow different filing rules, such as Form 1120-F.
Do I need to file Form 1120 if my corporation had no income?
Generally yes. Domestic corporations file whether or not they have taxable income, unless exempt or filing a special return.
When is Form 1120 due?
For calendar-year corporations, the 15th day of the fourth month after year-end. The 15 April 2026 date covers 2025. Form 7004 extends filing, not payment.
Does an Australian-owned U.S. company need to file Form 1120?
Usually, if it is classified as a domestic corporation. Form 5472, withholding, treaty, Australian reporting and related-party rules may also apply.
