How to File a CT Estate Tax Return: Deadlines and Penalties

To file a Connecticut estate tax return, the executor submits one of two forms within nine months of the decedent’s death: Form CT-706 NT if the Connecticut taxable estate is at or below the $15 million exemption for 2026, or Form CT-706/709 if it exceeds that amount or makes a Connecticut QTIP election. The nontaxable form goes only to the probate court. The taxable form goes to both the Department of Revenue Services and the probate court. Even estates that owe nothing generally need to file, because Connecticut places an automatic lien on the decedent’s real property that only lifts once the return is processed.

Pick the Right Form First

The choice between the two returns turns on the size of the Connecticut taxable estate and whether any Connecticut QTIP election is being made.

Form CT-706 NT is for nontaxable estates. If the taxable estate is at or below $15 million and no Connecticut QTIP election is made, this is the form to use. It is filed with the probate court only, not with the Department of Revenue Services. The probate judge reviews it and, if satisfied the estate falls below the exemption, issues Form PC-255 confirming no Connecticut estate tax is due. If the judge is not satisfied, the estate is sent back with instructions to file the full CT-706/709.¹

Form CT-706/709 is for taxable estates and for any estate making a Connecticut QTIP election. It is filed with both the Department of Revenue Services and the probate court.² The tax on a taxable estate is a flat 12% on every dollar above the federal basic exclusion amount.³

Nonresidents only trigger a Connecticut filing requirement if the decedent owned real estate or tangible personal property physically located in Connecticut at death. Resident decedents are taxed on the entire estate as valued for federal estate tax purposes.⁴

What Goes Into the Connecticut Taxable Estate

The Connecticut taxable estate is not just what the decedent owned on the date of death. It starts with the federal gross estate less allowable federal deductions, then adds back all Connecticut taxable gifts made from January 1, 2005 onward (excluding gifts already included in the federal gross estate), plus any Connecticut gift tax paid within three years of death.⁵ Gathering a complete gift history back two decades is often the hardest preparation task.

Connecticut follows federal rules for deductions. The unlimited marital deduction applies to property passing outright to a U.S. citizen spouse or into a qualifying trust. When no federal QTIP election was made, the executor can make a Connecticut-only QTIP election that treats certain trust property as qualifying for the marital deduction for state purposes.¹ Debts of the decedent, funeral expenses, and estate administration costs also reduce the gross estate. Once the tax is calculated, the estate receives a credit for any Connecticut gift tax already paid on the added-back lifetime gifts.³

One planning point matters at the return stage because it cannot be fixed after death: Connecticut does not allow portability of a deceased spouse’s unused exemption. Each spouse’s $15 million exemption is use-it-or-lose-it. If the first spouse left everything outright to the survivor, that first exemption is gone, and the survivor’s estate is measured against a single $15 million shield.

Documents and Valuation

The full return asks for the decedent’s legal name, Social Security number, and last permanent address to establish residency. You then need financial records supporting the value of every asset: bank statements, brokerage account balances as of the date of death, professional appraisals for real estate and business interests, and life insurance statements on Federal Form 712.⁶

Assets are valued at fair market value on the date of death. Because Connecticut defines the taxable estate by reference to the federal gross estate as valued for federal purposes, the alternate valuation date six months after death should also be available when the estate elects it for federal purposes.⁵

Separate probate assets from non-probate assets such as life insurance proceeds, jointly held accounts, and retirement accounts with named beneficiaries. Both categories count toward the taxable estate. If the estate also requires a federal Form 706, attach copies of the federal return and all supplemental documents to the Connecticut filing.²

Where to Submit the Return

Form CT-706/709 can be filed electronically through the myconneCT portal or by mail to the Department of Revenue Services. Electronic filing is not mandatory, but it provides immediate confirmation. You can file and pay through myconneCT without creating a permanent account.⁷

Whichever method you choose with the Department of Revenue Services, a copy of the return must also be submitted to the probate court with jurisdiction over the estate. The executor declares under penalty of law that this duplicate filing will occur simultaneously.² Form CT-706 NT, by contrast, goes only to the probate court.

Nine-Month Deadline and Extensions

The return is due nine months after the date of death. Any tax owed is due at the same time the return is filed, and the clock runs regardless of whether the executor has been formally appointed.

Form CT-706/709 EXT provides two extensions that can be requested separately. An extension to file grants an additional nine months, for a total of 18 months from death. An extension to pay grants six months beyond the original deadline, for a total of 15 months from death, and requires a statement of reasonable cause explaining why the estate cannot pay on time.⁸ The request must reach the Department of Revenue Services on or before the original nine-month deadline.

Extending the time to file does not extend the time to pay. If you need more time to finalize valuations but can estimate the tax, file the extension and pay the estimated amount to stop penalties and interest from accruing.

Penalties and Interest

A late payment penalty of 10% of the unpaid tax, or $50, whichever is greater, applies when the tax is not paid on time. A separate late filing penalty of 10% of the tax due, or $50, whichever is greater, applies when the return itself is late. The estate cannot be assessed both penalties for the same period.⁹

Interest accrues at 1% per month, or any fraction of a month, on unpaid tax from the original due date until payment. The Commissioner of Revenue Services can waive penalties when the executor demonstrates reasonable cause. Interest is not waivable.⁹

Releasing the Estate Tax Lien

Connecticut places an automatic lien on all real property owned by a decedent. Until the lien is released, the property cannot be cleanly sold or transferred to heirs, and this is why even nontaxable estates need to file.

For nontaxable estates, the probate court issues the release after reviewing Form CT-706 NT and determining the estate falls below the exemption.⁴ For taxable estates, the Department of Revenue Services issues a tax release or closing letter after processing Form CT-706/709 and verifying the tax has been paid. That document is then recorded in the land records to clear the lien.

When real property must be sold before the return is finalized, the executor can use Form CT-4422 UGE to request an early lien release from the probate court. Lien clearance is a prerequisite before the probate judge can issue a final decree of distribution.¹⁰

One boundary worth flagging: probate court fees are calculated separately on a sliding scale tied to estate size and apply even when no estate tax is owed.¹¹ Those fees are not part of the estate tax return itself, but they will show up on the same estate’s docket.

1
Connecticut State Department of Revenue Services. 2025 Form CT-706 NT Instructions
2
Department of Revenue Services. Connecticut Estate and Gift Tax Return
3
Justia. Connecticut Code 12-391 – Transfer of Resident and Nonresident Estates
4
Connecticut Department of Revenue Services. Form CT-4422 UGE – Application for Certificate Releasing Connecticut Estate Tax Lien
5
Connecticut State Department of Revenue Services. Estate and Gift Tax Information
6
Connecticut State Department of Revenue Services. Estate and Gift Tax
7
Connecticut State Department of Revenue Services. Filing and Paying
8
Department of Revenue Services. Form CT-706/709 EXT – Application for Estate and Gift Tax Return Filing Extension and Estate Tax Payment Extension
9
Justia. Connecticut Code 12-392 – Payment of Tax
10
Connecticut Probate Courts. Petition for Certificate Releasing Liens
11
Connecticut Probate Courts. Sec. 45a-107 – Fees and Expenses for Settlement of Decedent’s Estate