No, you do not have to pay any penalty if the IRS determines that your failure to timely file is due to reasonable cause.
Reasonable cause relief is the IRS's non-assertion or removal of certain civil penalties for failures related to filing information returns or IRS tax returns, making a deposit, or paying a tax, due to reasonable cause and not due to willful neglect. Reasonable cause is based on all the facts and circumstances in your situation. The IRS will consider any reason that establishes you exercised all ordinary business care and prudence to meet your annual filing obligations but were nevertheless unable to comply with a prescribed duty within the prescribed time.
For instance, under IRC § 6651, penalties for failure to file a tax return or to pay tax can be waived if the taxpayer can show that the failure was due to reasonable cause and not due to willful neglect. Specifically, IRC § 6651(a)(1) and (a)(2) provide that no penalty shall be imposed if the taxpayer can demonstrate reasonable cause for the failure and that they acted in good faith.
The IRS applies a facts and circumstances test on a case-by-case basis to determine whether a taxpayer meets the reasonable cause and good-faith exception. This involves evaluating the taxpayer's effort to report the proper tax liability, the nature of the tax, the complexity of the issue, the competence of the tax adviser, and other relevant factors such as the taxpayer’s experience, knowledge, education, and reliance on the advice of a tax adviser.
In summary, if you can demonstrate that your failure to comply was due to reasonable cause and not due to willful neglect, the IRS will not impose a penalty.
Sources:
§ 6651. Failure to file tax return or to pay tax
§ 6664. Definitions and special rules
IRM Part 20. Penalty and Interest. Chapter 1. Penalty Handbook. Section 1. Introduction and Penalty Relief
IRM Part 20. Penalty and Interest. Chapter 1. Penalty Handbook. Section 9. International Penalties
The Layman’s Guide to Reasonable Cause With the IRS
