It's ultimately your responsibility to pay your quarterly taxes. If the client didn't send them to the IRS quarterly, then you "may" be assessed an underpayment penalty for not having paid each quarter. You can pay your quarterly taxes online at http;//<a rel="nofollow" target="_blank" href="
http://www.irs.gov/payments">www.irs.gov/payments</a>. The sooner you pay, the sooner your penalty stops increasing.
