there should be an estimated tax worksheet for computing 2021 using 1 of the standard rules.
1) 100 % of 2020 tax (110% if adjusted gross income over $150,000
or
2) 90% of 2021 tax - good luck trying to figure our what this will be
or
3) the annualized installment method - don't know if your version of turbotax handles this
you figure your actual income for the 1st 3, then 5, then 8 months and then the whole year
you annualize the income x4, x2.4 x1.5,x 1
you figure the tax on this income and also any other taxes such as self-employment taxes and any credit subject to what ever limitations there are
you multiply your total taxes for each period by 22.5%,45% 67.5% and 90%
then you subtract from this any withholding for the period and any prior tax payments, what's left is the estimated tax payment for the quarter.
you may want to use form 2210 schedule AI
of course, if you make an error you could be subject to penalties.
option 1 is the safest because that's based on line 24 of the 2020 return.
1/4 each quarter.
