How long do I have to respond to IRS CP103?

Contact the IRS within 60 days if you disagree. Use the deadline printed on your notice and verify how it is calculated. IRS deadlines may run from the notice or mailing date and are not automatically extended because the letter arrived or was opened late.

What should I do if I received IRS CP103?

Compare the notice with your return, then pay by the coupon date or call or write the IRS within 60 days if you disagree. If you are unsure, have a tax professional review the letter before you respond to the IRS.

IRS CP103 Notice: Miscalculation Changed Your Balance Due

The IRS found a miscalculation on your return and your balance due changed. Pay by the coupon date, or contact the IRS within 60 days if you disagree.

Published by the Law Offices of Darrin T. Mish, P.A.Updated October 13, 2026

Notice: CP103
Urgency: Urgent
Deadline: Contact the IRS within 60 days if you disagree

Your first move

Compare the notice with your return, then pay by the coupon date or call or write the IRS within 60 days if you disagree.

A CP103 notice means the IRS changed your tax return because it found a miscalculation. Your balance due changed as a result. The notice explains why you owe.

What to Do

Read the notice carefully.
Compare its figures with your return.
If you agree, correct the copy of the return you kept and pay the amount due by the date on the payment coupon.
If you disagree, contact the IRS within 60 days of the notice date.

If You Disagree

Call the number on your notice or write to the address on the contact stub within 60 days. The IRS may be able to reverse the change.

If you can't provide additional information that justifies a reversal, the IRS will forward your case for audit. That step gives you formal appeal rights, including the right to appeal the decision in court before you have to pay the additional tax. The audit staff will contact you within 5 to 6 weeks to explain the audit process and your rights.

If You Miss the 60 Days

You lose your right to appeal before you pay. To dispute the change after that, you have to pay the tax and then file a claim for refund. The claim must be filed within 3 years of the date you filed the return, or within 2 years of the date of your last payment of this tax.

If You Can't Pay

Call the toll-free number on your notice to discuss payment options, or apply online for a payment plan, including an installment agreement.

Interest: None if you pay in full by the due date on the coupon. After that, interest accrues on the unpaid balance.
Penalty: If you can't pay in full, you'll get a late payment penalty. If circumstances beyond your control are the reason, contact the IRS by the payment due date. Depending on your situation, the penalty may be removed.

Next Time

File electronically if you can, and review your return for accuracy before you send it. Keep this notice and copies of anything you send in response.

If you received a CP103 notice and want to challenge the change or set up payments, call us at (813) 229-7100.

This letter has a clock on it. Don’t run it out alone.

Free consultation with Darrin T. Mish, a Tampa tax attorney licensed since 1993 and admitted to the U.S. Tax Court. Bring the letter.

Call (813) 229-7100

Request a consultation online