Quinnipiac Lighting has thirteen Connecticut sales-tax dates, five of them not the last day of the month

The moment

Quinnipiac Lighting is a lighting showroom in Hamden, Connecticut: chandeliers, lamps and a few designer fixtures, sold to homeowners and to the contractors who come in for the trade counter. Marisol Tran bought it in 2017. It has three W-2 employees besides Marisol, it is taxed as an S corporation, and it collects Connecticut sales tax at the register. It is the third of October, the holiday lighting rush is five weeks off, and Marisol is writing next year's dates on the office wall.

What they did instead

Marisol's habit was the end of the month. Sales tax, the last day, every month. That is the right rule. It fails on the days the last day is a Saturday or a Sunday, and in the next year that is five of the thirteen. The Department's sales-tax page does not say what happens then, so the habit has no answer, and the usual one is to file on the Friday before and hope it was early enough. The other hole is January. The first return of the year lands on the same day as the payroll year-end filings, and nobody had them on one sheet.

The questions a CFO asks first

1. How many Connecticut dates does the shop have in the next year, and which of them are not the last day of the month?
2. Which of those moves does the Department actually confirm?
3. What changes if Connecticut has the shop on a quarterly schedule instead of monthly?
4. What does the sheet leave off, and does the entity type change what Connecticut adds?

The arithmetic, shown

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

Scenario one: monthly, the schedule the shop is on. The Department of Revenue Services' sales-tax page states

> Form OS-114 is due on or before the last day of the month following the end of the filing period.

The tool returns twenty-three dated line items. Thirteen are Connecticut sales-tax returns, January 2026 through January 2027. The other ten are federal: the owner's four estimates, four Form 941 payroll returns, Form 940 and the W-2s. There is no Connecticut estimate on the sheet. That is the tool's choice, not an answer, and the page comes back to it below.

Connecticut states its dates as a rule, so the tool works each one out. Eight of the thirteen are the last day of the month as it falls: March 31, April 30, June 30, July 31, August 31, September 30, November 30 and December 31. Five are not. January 31, 2026 is a Saturday, so the return is dated

> 2026-02-02

February 28 is a Saturday, so

> 2026-03-02

May 31 is a Sunday, so

> 2026-06-01

October 31 is a Saturday, so

> 2026-11-02

and the last return, for December 2026, falls on January 31, 2027, a Sunday, so it is dated

> 2027-02-01

Here is the caution. The tool moves those five off the weekend, and it tells the owner the Department did not write that rule on this page:

> the Department's corporation and income-tax pages say a Saturday, Sunday or legal holiday moves a due date to the next business day, but its sales-tax page does not repeat that, so check myconneCT before relying on a sales-tax date this tool moved off a weekend (in 2026 and early 2027: January 31 to February 2, February 28 to March 2, May 31 to June 1, October 31 to November 2, and January 31, 2027 to February 1).

The rule is written on two other Department pages and the tool applies it here. Whether it holds for a sales-tax return is the question for the myconneCT account, and the five dates are the ones to check.

The crowding is small and it is in one place. February 2 carries four items: the January sales-tax return, the fourth-quarter Form 941, Form 940 and the W-2s. April 30, July 31 and November 2 carry two each, a sales-tax return and the federal quarterly Form 941. No Connecticut date shares a day with the owner's federal estimates.

Scenario two: quarterly. The tool returns fourteen items, not twenty-three, with four Connecticut returns dated 2026-04-30, 2026-07-31, 2026-11-02 and 2027-02-01. Nine fewer lines. It assumes a quarterly filer files on calendar quarters, which is its own assumption.

Scenario two (b): annual. The tool returns eleven items and one Connecticut return, dated 2027-02-01.

Scenario two (c): a schedule the tool does not date. If the shop is on something else, or is not sure, the tool returns ten items: the federal ones, no Connecticut date at all. It says

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

and sends the owner to the myconneCT account for the schedule Connecticut 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 Connecticut 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-three. Federal Form 1120 and four Form 1120-W deposits arrive in place of the owner's four estimates, and four Connecticut corporation business tax installments arrive. The Department's corporation page states

> First: fifteenth day of the third month of the income year. Second: fifteenth day of the sixth month. Third: fifteenth day of the ninth month. Fourth: fifteenth day of the twelfth month.

For a calendar-year corporation that is March 15, June 15, September 15 and December 15. March 15, 2026 is a Sunday, so the first payment is dated

> 2026-03-16

a month before any federal date, and the last is

> 2026-12-15

The thirteen sales-tax returns do not move. Seventeen Connecticut lines in all. March 16 carries only the Connecticut payment, and April 15, June 15, September 15 and December 15 each carry two items, the federal and the Connecticut one.

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 Connecticut installments. The thirteen sales-tax returns stay. The tool gives the reason:

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

What changed

Marisol has thirteen Connecticut dates on the same sheet as the federal payroll and estimated-tax dates. The last day of the month on the wall is right for eight of the thirteen returns. The numbers to watch are five and four: five returns that a habit of the last day files on a weekend, and four items on the one morning in February. The five are also the five the Department's own sales-tax page is silent on, which is why the myconneCT account is the place to confirm them.

What the tool will not do

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

> This tool doesn't cover Connecticut's individual estimated-tax dates (Form CT-1040ES; no Department of Revenue Services page this run could read gave them, so none are shown), the corporation business tax return or its extended date, withholding, pass-through entity tax, or local taxes.

That is not a statement that none are due. Quinnipiac is an S corporation, and an owner of one may have Connecticut estimated tax of their own to pay. The sheet shows no Connecticut estimate date because the tool could not read the page that gives one, not because there is none. Connecticut withholding on three people's wages and the pass-through entity tax are not on the sheet either. 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.