When a fiduciary combines a qualified revocable trust with the decedent’s estate under a Section 645 election, the combined entity files under a single Employer Identification Number. If an executor has been appointed, that EIN is the estate’s. If no probate estate exists, the trustee obtains an EIN for the trust to use as the electing entity. Either way, one EIN covers both the trust and estate for the length of the election, and a new EIN is needed for the trust once the election ends. This is the practical guidance on the EIN for a combined trust and estate.
Which EIN the Combined Entity Uses
The answer depends on whether an executor exists.
When an executor has been appointed and the estate has its own EIN, that estate EIN is used on all tax filings for the combined entity. The trust stops using whatever identification number it had before, whether that was the decedent’s Social Security number or a separately obtained EIN. All income from both the estate and the trust gets reported under the estate’s number on a single Form 1041.1eCFR. 26 CFR 1.645-1 – Election by Certain Revocable Trusts to Be Treated as Part of Estate
When there is no executor and no probate estate exists, the trustee obtains an EIN for the trust that reflects its status as the electing entity. The trust steps into the estate’s shoes for income tax purposes and files the combined return under that number.1eCFR. 26 CFR 1.645-1 – Election by Certain Revocable Trusts to Be Treated as Part of Estate
One EIN, one Form 1041. If a trust EIN was already pulled before the decision to elect was made, it simply drops out of use once the estate’s EIN takes over.
Applying for the EIN
Whether you need an estate EIN at the start of administration or a trust EIN because there is no probate estate, the application is the same Form SS-4 process.
Information You Need Before Applying
The IRS asks for the following:
- Legal name of the entity as it appears in the governing documents.
- Responsible party. For an estate, this is the executor or personal representative; for a trust, it is the grantor, owner, or trustee. The responsible party must be an individual, not another entity.2Internal Revenue Service. Responsible Parties and Nominees
- The responsible party’s Social Security number or ITIN, which the IRS uses to link the new entity to a real person.
- Date the entity was funded or the decedent died, which establishes when the entity came into existence for tax purposes.
- Entity type. The IRS distinguishes between estates, testamentary trusts, and irrevocable trusts, and the classification affects which tax rules apply.
A beneficiary who is entitled to receive trust property but has no authority to manage or direct the entity cannot serve as the responsible party. This comes up often with minor children named as trust beneficiaries.2Internal Revenue Service. Responsible Parties and Nominees
How to Submit the Application
The IRS online application is the fastest route and issues the EIN immediately. It is available Monday through Friday from 6:00 a.m. to 1:00 a.m. Eastern, Saturday from 6:00 a.m. to 9:00 p.m., and Sunday from 6:00 p.m. to midnight.3Internal Revenue Service. Get an Employer Identification Number
Fiduciaries who prefer paper can fax Form SS-4 and typically receive the EIN within four business days, or mail it to the IRS service center in Cincinnati, Ohio, which takes roughly four to five weeks.4Internal Revenue Service. Instructions for Form SS-4 Save the confirmation notice. Banks and brokerage firms will ask for it before opening fiduciary accounts or retitling assets.
An attorney or accountant can be authorized to receive the EIN on the fiduciary’s behalf through the third-party designee section of Form SS-4. That authority ends the moment the EIN is assigned. If the designee’s address or phone number matches the taxpayer’s, the online application will not process the form and it has to be submitted by fax or mail.4Internal Revenue Service. Instructions for Form SS-4
Making the Section 645 Election Official
The EIN choice only holds up if the election itself is properly filed. A qualified revocable trust is one the decedent controlled during their lifetime through a power to revoke or amend. After death it normally becomes a separate taxable entity, but Section 645 lets the executor and trustee jointly elect to treat it as part of the estate for federal income tax purposes.5Office of the Law Revision Counsel. 26 USC 645 – Certain Revocable Trusts Treated as Part of Estate Where no probate proceeding exists, the trustee alone makes the election and treats the trust as if it were an estate for income tax purposes during the election period.1eCFR. 26 CFR 1.645-1 – Election by Certain Revocable Trusts to Be Treated as Part of Estate
The election is made on Form 8855. Once filed, it is permanent and cannot be revoked.6Internal Revenue Service. About Form 8855, Election to Treat a Qualified Revocable Trust as Part of an Estate It must be filed by the due date of the estate’s first Form 1041, including extensions, even if the combined entity does not have enough income to require a return.7Internal Revenue Service. 2025 Instructions for Form 1041 and Schedules A, B, G, J, and K-1 If an executor exists, both the executor and the trustee of each qualifying revocable trust must sign under penalties of perjury. When there is no executor, only the trustee signs.1eCFR. 26 CFR 1.645-1 – Election by Certain Revocable Trusts to Be Treated as Part of Estate
The election period runs for two years after the date of death when no federal estate tax return is required. When a Form 706 is required, it continues until six months after the IRS makes a final determination on estate tax liability.5Office of the Law Revision Counsel. 26 USC 645 – Certain Revocable Trusts Treated as Part of Estate
A New EIN After the Election Ends
When the election period closes, the trust is treated as receiving a deemed distribution from the combined entity and becomes a separate trust for tax purposes. That trust generally needs its own taxpayer identification number.1eCFR. 26 CFR 1.645-1 – Election by Certain Revocable Trusts to Be Treated as Part of Estate
If the estate continues after the election terminates, it keeps the same EIN it used all along. The trust, now filing separately, must switch to a calendar year regardless of what fiscal year the combined entity had been using. That switch can create a short tax year for the trust. Banks and brokerage firms holding trust assets will need the new TIN to update their records and issue correct 1099s, so plan for the paperwork before the election lapses rather than after.
Filing Threshold and Late Penalty
An estate must file Form 1041 when it has gross income of $600 or more for the tax year. The same $600 threshold applies to trusts, and trusts must also file if they have any taxable income regardless of the gross amount.8Office of the Law Revision Counsel. 26 USC 6012 – Persons Required to Make Returns of Income Almost any income-producing asset will clear that bar.
A late return triggers a penalty of 5% of the unpaid tax for each month or partial month the return is late, up to a maximum of 25%.9Internal Revenue Service. Failure to File Penalty For a fiscal year entity, the Form 1041 due date is the 15th day of the fourth month after the fiscal year ends. Calendar it as soon as the EIN is in hand.