New York State's estate tax is calculated using the tax table provided on Form ET706. There are multiple versions of Form ET-706.You must file Form ET-706 within nine months after the decedent's date of death, unless you receive an extension of time to file the return. The income tax return form for estates is IRS Form 1041. It's also called a "fiduciary" return, because you file it in your capacity as executor of the estate. An estate tax return is generally due 9 months after the decedent's death. So, 9 months after the date of death. All required New Jersey Estate Tax returns must be filed within nine (9) months of the date of a resident decedent's death. To e-file a document, use your Electronic Filing Service Provider.