How do I calculate the amount of interest that is due on my late tax return?

Interest is calculated using the following formula: (Original liability x Rate x # of days delinquent divided by 365.25)

Example: Assume the liability on an entity’s monthly sales tax return for February is $1,000. This return was due by March 20, but was not filed until April 22 (33 days late). The interest rate, effective July 1, 2017, through June 30, 2018, is 8% (The interest rate from July 1, 2016 through June 30, 2017 is 7.5%). Interest is calculated as follows:

$1,000 x 8% x 33 divided by 365.25 = $7.23.