the 2210 penalty for underpaying your estimated taxes is from 4% to 7% based on the period and number of days late. see worksheet for 2210 on page 7 of the instructions. https://www.irs.gov/pub/irs-pdf/i2210.pdf
the failure to file penalty is 5%/ month for a maximum of 5 months (filing after the due date and owing). the failure to pay penalty is .5% a month and applies when the balance due is paid after the original due date.
if both penalties apply to a period the failure to file penalty is reduced to 4.5%
