During the grantor's lifetime, a revocable trust typically does not require its own EIN. The grantor may use their Social Security Number (SSN) to report all trust income, deductions, and credits on their individual Form 1040, and the trust itself does not file Form 1041. The trustee furnishes the grantor's SSN to payers of income.

However, when the grantor dies, the revocable trust becomes irrevocable. At that point, the trust is treated as a new, separate taxable entity and must obtain an EIN. The IRS requires an EIN to be assigned when "the trust becomes irrevocable following death."

There is a limited exception during the settlement period immediately after death. A revocable trust that becomes irrevocable upon the grantor's death is not considered a charitable trust under section 4947(a)(1) or a split-interest trust under section 4947(a)(2) for a reasonable period of settlement after becoming irrevocable. This settlement period is the time reasonably required (or actually required, if shorter) to perform ordinary administrative duties such as collecting assets, paying debts and taxes, making distributions, and determining beneficiary rights.2 During this brief window, certain excise tax provisions may not apply, but the trust still requires an EIN as a separate entity.

After the settlement period, the trust is fully subject to the applicable trust tax rules and must file Form 1041 using its own EIN.

In short, a revocable trust needs its own EIN once the grantor dies and the trust becomes irrevocable, even though a short administrative settlement period may apply for certain purposes.