We are truly sorry to hear about your loss.
With respect to your tax question, if you have an EIN for your spouse's estate, and you are asking about filing Form 1041 (an estate income tax return), then in that instance you would want to use the EIN.
If you are instead asking about your personal income tax return (Form 1040 series), then you should use your spouse's SSN here, not an EIN.
The following information from IRS Publication 17 may be helpful as well:
"If your spouse died during the year, you are considered married for the whole year for filing status purposes.
'If you didn't remarry before the end of the tax year, you can file a joint return for yourself and your deceased spouse. For the next 2 years, you may be entitled to the special benefits [by filing as a] Qualifying Widow(er) With Dependent Child .
'If you remarried before the end of the tax year, you can file a joint return with your new spouse. Your deceased spouse's filing status is married filing separately for that year."
Thank you for asking this question.
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