Is my tax preparer liable for mistakes on my return?

My tax preparer put my "taxes due" amount on the "estimated taxes" line and the IRS has returned my payment because of that and subsequently billed me for the amount due plus interest. I'm sure that I can get the IRS to credit my payment properly, but if they won't waive the interest is my tax preparer liable for it?
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No, he is not. While many will cover the penalties (and occasionally the interest) due to their error, they are under no LEGAL obligation to do so.

Keep in mind that if he does cover any penalties and/or interest, you must report that as income on your return next year on line 21 as Other Income.
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If the IRS sent you a check for the money that you paid them then you have sufficient proof to have the penalties and interest on that amount removed as of the date that you mailed the payment. It will take a human to override the system though. TFTP. Report Abuse

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I'm hard pressed to believe that the IRS returned that check like you say.

The IRS computer is coded to not trust the estimated tax line. The account doesn't use the number from the tax return. Instead it uses the amount shown on the account itself.

On the other hand, I would believe that your preparer put the wrong number on the withholding line and verified it later with the W-2.
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Here's what I would do...
1. Call your tax agent and explain their mistake to them - ask them to organise to have the interest waived at no cost to you. If the interest cannot be waived, ensure they pay for it. Any reasonable tax agent will be happy to rectify their error.
2. Find a new tax agent.
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Liable in what sense? Can you sue him for it? Possibly. I would HOPE that any qualified professional would offer to cover the interest himself. I know that H&R Block offers that as a guarantee.
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You are responsible for whatever you owe. A preparer who makes a mistake that costs you a penalty could offer to pay the penalty.