Maine Form 1120ME is the annual corporate income tax return filed with Maine Revenue Services by every taxable C-corporation with a Maine connection. It starts from federal taxable income, applies Maine modifications, apportions the result using a single-sales-factor formula, and applies graduated rates from 3.5 percent to 8.93 percent.1Maine Revenue Services. Corporate Income Tax (1120ME) Calendar-year filers owe the return by April 15, and Maine grants an automatic six-month filing extension with no written request needed.
Who Has to File
Under 36 M.R.S. § 5200, Maine taxes the net income of every corporation with nexus in the state.2Maine State Legislature. Maine Code 36 5200 – Imposition and Rate of Tax Two categories are carved out: financial institutions that pay Maine’s franchise tax, and insurance companies that pay the premiums tax.1Maine Revenue Services. Corporate Income Tax (1120ME) Every other C-corporation doing business in Maine uses Form 1120ME. Tax-exempt organizations with unrelated business income file the form to report that income.3Maine Revenue Services. Corporate Income Tax FAQ
A corporation organized or commercially headquartered in Maine has nexus automatically. An out-of-state corporation has nexus if any one of these thresholds is crossed in the tax year:4Maine State Legislature. Maine Code 36 Section 5200-B – Corporate Income Tax Nexus
- $250,000 of property in Maine
- $250,000 of payroll in Maine
- $500,000 of sales in Maine
- 25 percent of total property, payroll, or sales in Maine
Crossing one line is enough. Physical presence is not required.
If your corporation belongs to an affiliated group operating a unitary business (shared ownership, centralized management, integrated operations) and at least one member has Maine nexus, the group must file a combined report with the return, and each Maine-nexus member files its own Form 1120ME. Maine uses a water’s-edge combined base.5Maine Revenue Services. Maine Unitary Business Taxable Income, Combined Reports, and Tax Returns
What You’ll Pay
Maine’s corporate income tax is graduated. For tax years beginning on or after January 1, 2018:2Maine State Legislature. Maine Code 36 5200 – Imposition and Rate of Tax
- 3.50% on taxable income up to $350,000
- 7.93% on taxable income from $350,001 to $1,050,000
- 8.33% on taxable income from $1,050,001 to $3,500,000
- 8.93% on taxable income over $3,500,000
The rates apply to Maine net income after apportionment, not to income everywhere. A multistate company with $5 million in total income but only 20 percent of its sales in Maine applies these rates to roughly $1 million.
Filling Out the Return
You need a completed federal Form 1120 first. The Maine return uses federal taxable income as its starting point, then layers on state modifications, apportionment, and credits.6Maine Revenue Services. Maine Corporate Income Tax Form 1120ME Instructions
Maine Modifications
Maine requires specific additions and subtractions to federal taxable income. The most common addition is state income tax deducted at the federal level, because Maine does not allow a deduction for its own tax. On the subtraction side, interest from certain exempt obligations may be deducted. These modifications appear on the form before the apportionment step and produce the base for apportionment.
Apportionment
Corporations that earn income both inside and outside Maine apportion using a single sales factor. Divide Maine sales by total sales everywhere to get a percentage, then multiply that percentage by modified income. A corporation with 30 percent of its sales going to Maine customers apportions 30 percent of its income to the state. The older three-factor formula (property, payroll, sales) is no longer the standard method.
Credits
After tax is calculated, credits reported on Schedule C reduce the liability. Available credits include:6Maine Revenue Services. Maine Corporate Income Tax Form 1120ME Instructions
- Seed capital investment tax credit for investing in a qualifying Maine business through the Finance Authority of Maine
- Pine Tree Development Zone credit for new or expanded businesses certified by the Department of Economic and Community Development
- Research expense tax credit for qualified research spending
- Maine capital investment credit for property eligible for federal bonus depreciation
- Employer credit for family and medical leave wages paid to Maine-based employees
Each credit has its own eligibility rules and documentation. Some, like the employer-assisted day care credit, are only available as carryforwards from prior years. Gather proof of each credit before you file; missing documentation is one of the fastest ways to stall processing.
Deadlines and the Automatic Extension
The return is due on the fifteenth day of the fourth month after the tax year ends. For calendar-year filers that means April 15. A June 30 fiscal year end pushes the due date to October 15.3Maine Revenue Services. Corporate Income Tax FAQ
Maine grants an automatic six-month extension to file with no written request. You just file within six months of the original due date. The extension covers filing only. Any tax owed is still due by the original date, and you should use Form 1120EXT-ME as a payment voucher, or pay through the Maine Tax Portal to skip the voucher.7Maine Revenue Services. Maine Extension Tax Payment Voucher for Corporations
If the IRS grants a federal extension beyond six months, Maine automatically matches the federal date plus 30 days, provided you attach proof of the federal extension to your Maine return. The total Maine extension generally cannot exceed eight months.3Maine Revenue Services. Corporate Income Tax FAQ
Quarterly Estimated Payments
Corporations that expect to owe more than a minimal amount of Maine tax must pay quarterly during the tax year. For calendar-year filers, installments are due April 15, June 15, September 15, and January 15 of the following year. Fiscal-year filers shift the dates to their own year-end. You can pay in four equal installments or in full with the first. Form 2220ME calculates any underpayment penalty when you file the annual return.8Maine Revenue Services. Corporate Income Tax Forms
Submitting the Return
Maine Rule 104 requires certain corporations to file electronically. If electronic filing creates genuine hardship, you can request a waiver in writing from the State Tax Assessor, explaining why and when you expect to comply.3Maine Revenue Services. Corporate Income Tax FAQ
The main electronic option is Modernized e-File through approved tax software, which submits federal and state returns together.9Internal Revenue Service. Modernized e-File (MeF) Internet Filing The Maine Tax Portal is the state’s direct interface for returns and payments.10Maine Revenue Services. Electronic Services Electronic returns process faster and give you immediate confirmation of receipt.
If you file on paper, the address depends on whether you’re enclosing a payment:11Maine Revenue Services. Mailing Addresses for Forms and Applications
- With payment: Maine Revenue Services, P.O. Box 1065, Augusta, ME 04332-1065
- Without payment: Maine Revenue Services, P.O. Box 1064, Augusta, ME 04332-1064
Using the wrong box won’t void your return, but it slows processing while staff reroute it. Check the address before sealing the envelope.
Penalties and Interest
Missing the filing deadline or underpaying triggers penalties and interest that grow quickly.
Late filing. If the tax owed is more than $25 and you file late but before Maine Revenue Services issues a formal demand (or within 60 days of one), the penalty is $25 or 10 percent of the unpaid tax, whichever is greater. If you still haven’t filed within 60 days after a formal demand, the penalty rises to $25 or 25 percent of the tax due.12Maine State Legislature. Maine Code 36 187-B – Penalties
Late payment. When the return is filed on time but tax isn’t fully paid, the penalty is 1 percent of the unpaid balance per month (or partial month), capped at 25 percent.12Maine State Legislature. Maine Code 36 187-B – Penalties
Interest. Interest accrues on unpaid tax from the original due date and compounds monthly. For 2026, the annual rate is 9 percent, down from 10 percent in prior years. The State Tax Assessor sets the rate annually, so confirm the current rate for the period you’re filing.
The extension waives the late-filing penalty but does nothing for interest or the late-payment penalty; both accrue from day one. Paying what you owe by the original due date, even if the return isn’t finished, is the fastest way to limit the damage.