there is a penalty for underpaying estimated taxes form 2210 (see form 2210 and the instructions for the computation of this penalty), a penalty of .5%/month for paying after the normal due date. in addition, when paying after the normal due date there is currently an 8% interest charge which is compounded daily. it consists of the federal short-term interest rate of 5% + an added 3%. the rate changes every 3 months
https://www.irs.gov/payments/quarterly-interest-rates
it seems you are asking about the 2210 penalty only
