Penobscot Marine Supply has seventeen Maine dates in 2026, and four days when three payments land at once

The moment

Penobscot Marine Supply is a chandlery in Rockland, Maine: rope, fittings, foul-weather gear and charts for the lobster boats and the summer sailboats on the harbour. Walt Pelletier bought it in 2018. It has two W-2 employees besides Walt, it is taxed as an S corporation, and it collects Maine sales tax at the counter. It is the third of October, the summer boats are coming out of the water, and Walt is putting next year's dates on the wall.

What they did instead

Walt's habit was the 15th. Sales tax, the 15th, every month. For nine of the thirteen dates in the next year that is the right day. The habit has two holes. The first is the four months when the 15th is not a business day. The second is worse: the 15th is also the day Walt's own estimated tax is due, in April, June, September and January, and Maine's estimate is due the same day. In those four months one afternoon carries three payments, and nobody had them on one sheet.

The questions a CFO asks first

1. How many Maine dates does the shop have in the next year, and which of them are not the 15th?
2. On how many days does Maine land on top of another item?
3. What changes if Maine has the shop on a quarterly schedule instead of monthly?
4. What does the sheet leave off, and does the entity type change what Maine adds?

The arithmetic, shown

Eight engine runs, all through the tool's own engine, all built on Penobscot's profile: an S corporation, two W-2 employees, no 1099 contractors, Maine as the state, registered to collect Maine sales tax.

Scenario one: monthly, the schedule the shop is on. Maine Revenue Services' rates and due dates page states

> Returns are due no later than the 15th of the month.

and its list of forms and due dates adds

> If the due date falls on a holiday or weekend, the due date is the next business day.

The tool returns twenty-seven dated line items. Seventeen are Maine: thirteen sales-tax returns, January 2026 through January 2027, and four individual estimated-tax installments. The other ten are federal: the owner's four estimates, four Form 941 payroll returns, Form 940 and the W-2s. Maine states its dates as a rule rather than a dated table, so the tool works each one out. It says so:

> Maine states these as rules (the 15th of a month) rather than a dated table, so this tool worked out each date and moved any that fall on a Saturday, Sunday or holiday to the next business day, as Maine Revenue Services says. In 2026 that moves February 15 to Tuesday, February 17 (Monday the 16th is Presidents' Day), March 15 to March 16, August 15 to August 17 and November 15 to November 16.

Nine of the thirteen returns are the 15th itself. Four are not. February 15, 2026 is a Sunday and the Monday after it is Presidents' Day, so the return is dated

> 2026-02-17

March 15 is a Sunday, so

> 2026-03-16

August 15 is a Saturday, so

> 2026-08-17

and November 15 is a Sunday, so

> 2026-11-16

The last return, for December 2026, is dated 2027-01-15, a Friday. The tool is also plain about what it did not check:

> This run did not check Maine's own state holiday list beyond those; no other date computed here is a federal holiday.

Now the part that matters more. Maine's page lists the individual estimate as

> Individual Income Tax: 1040ES-ME April 15, June 15, September 15, January 15. Corporate Income Tax: 1120ES-ME April 15, June 15, September 15, December 15.

Those are the same days as the federal estimate. The sales-tax return is also due on the 15th. So on April 15, June 15, September 15 and January 15, 2027, the sheet carries three items each: the federal installment, the Maine installment and the Maine sales-tax return. Four days, twelve items. Compare February 2, the other crowded day: three federal items and no Maine date on it. The tool adds a caution about the Maine installment:

> This tool doesn't ask whether a Maine estimated payment is actually owed, so it shows the schedule that would apply if one is.

Scenario two: quarterly. The page's table puts the first quarter's return in April, the second in July, the third in October and the fourth in January. The tool returns eighteen items, not twenty-seven, with four Maine returns dated 2026-04-15, 2026-07-15, 2026-10-15 and 2027-01-15. Nine fewer lines. The crowding does not go away: April 15 and January 15 still carry three items each, and June 15 and September 15 carry two.

Scenario two (b): semiannual. July and January. The tool returns sixteen items and two Maine returns, dated 2026-07-15 and 2027-01-15.

Scenario two (c): annual. January. The tool returns fifteen items and one Maine return, dated 2027-01-15.

Scenario two (d): a schedule the tool does not date. If the shop is on something else, or is not sure, the tool returns fourteen items: the federal ones and Maine's four estimates, no Maine sales-tax date at all. It says

> This tool doesn't compute a specific date for a Maine sales-tax filing frequency other than monthly, quarterly, semiannual or annual, or one that isn't confirmed.

and sends the owner to the Maine Tax Portal account for the schedule Maine assigned.

Scenario three: the frequency not yet confirmed. With everything else answered and the filing frequency left blank, the tool does not guess. It returns a named refusal: missing: ["how often Maine has this business file sales tax"]. Nothing computes until there is an answer.

Scenario four: the identical profile as a calendar-year C corporation. The tool returns twenty-eight items, not twenty-seven. Federal Form 1120 and four Form 1120-W deposits arrive in place of the owner's four estimates, and four Maine corporate installments arrive in place of the four individual ones. The thirteen sales-tax returns do not move. The crowding changes shape: April 15 carries four items (Form 1120, the first Form 1120-W deposit, Maine's first corporate installment and the sales-tax return), and June 15, September 15 and December 15 carry three each. The last corporate installment is

> 2026-12-15

a month before the S corporation's last individual one, and January 15, 2027 carries only the sales-tax return.

Scenario four (b): the same corporation, tax year unconfirmed. Mark the tax year as not calendar-year, or as unconfirmed, and the tool returns nineteen items. Nine dates disappear: Form 1120, the four 1120-W deposits and the four Maine corporate installments. The thirteen sales-tax returns stay. The tool gives the reason:

> This tool only computes Maine corporate dates for a calendar-year C corporation (tax year January-December).

What changed

Walt has seventeen Maine dates on the same sheet as the federal payroll and estimated-tax dates. The 15th on the wall is right for nine of the thirteen returns. The numbers to watch are four and four: four returns that a habit of the 15th files on the wrong day, and four days when that habit has three payments due at once.

What the tool will not do

It will not decide which schedule the shop is on. Maine Revenue Services assigns it, so the tool asks and builds dates from the answer. It will not compute the tax owed on any return or any installment. And for Penobscot specifically, the sheet is shorter than the real year. The tool's own note says what is off it:

> This tool doesn't cover Maine's corporate income tax return or its extended date, withholding, pass-through returns (S corporation and partnership), service provider or meals taxes, or local taxes.

That is not a statement that none are due. Penobscot is an S corporation with two employees, so the Maine pass-through return and Maine withholding on two people's wages are not on the sheet. A shop in a harbour town may also have other Maine taxes the tool does not date. The tool will not know about an extension, a payment plan or a penalty already assessed on any date above. This tool supports a named list of states, which the state picker in the tool shows, and every line above is the plain due date for the entity type it was told about.