See https://www.irs.gov/instructions/i1041#idm140229122357664
Generally, an estate or trust must pay estimated income tax for 2021 if it expects to owe, after subtracting any withholding and credits, at least $1,000 in tax, and it expects the withholding and credits to be less than the smaller of:
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90% of the tax shown on the 2021 tax return, or
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100% of the tax shown on the 2020 tax return (110% of that amount if the estate's or trust's adjusted gross income on that return is more than $150,000, and less than 2/3 of gross income for 2020 or 2021 is from farming or fishing).
However, if a return was not filed for 2020 or that return didn't cover a full 12 months, item 2 doesn't apply.
