Can I claim a deduction for paying previous years installment agreement taxes last year.

[ee-ea]

For federal taxes you can not  For state taxes you can .

[Mike9241]

to clarify. state taxes but not any penalties and interest paid in 2020 regardless of the year they're for would be deductible for federal purposes but not for state purposes.   a few states allow a deduction of federal taxes paid but again not penalties or interest in computing the state's income taxes.