What year 1041 estate tax form should be used for a estate starting 7-2017 and ending 7-2018?

Estate started in July 2017 and ended in July 2018.  What tax year form for the 1041 Estate Return should be filed - an estate form for 2017 for the 1041 or an estate form for 2018 for the 1041?

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You have a 2017 1041 initial return and a 2018 1041 final return.
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