IRS NOTICE REFERENCE
Understanding your CP173 notice
We assessed a penalty for failure to make sufficient timely estimated tax payments because our records show you didn't prepay enough of your tax through estimated tax payments or didn't make them on time. Corporations ge…
General information only. Not legal or tax advice.
Notice details
- Notice code
- CP173
- Category
- Penalty
- Severity tier
- Tier 2 — Action or response expected. The IRS has taken or proposed an action and expects a response or payment.
- Governing law
- §6651; §6662; §6751 (Internal Revenue Code sections)
- Source
- IRS.gov — Understanding Your IRS Notice
What this notice is
We assessed a penalty for failure to make sufficient timely estimated tax payments because our records show you didn't prepay enough of your tax through estimated tax payments or didn't make them on time. Corporations generally must make estimated tax payments if they expect to owe tax of $500 or more when their return is filed.
Source: IRS.gov. Reproduced for reference. General information — not legal or tax advice.
What the IRS says to do
Read your notice carefully. It will explain how much you owe and how to pay it. Pay the amount you owe by the due date on the notice. If you receive income unevenly during the year, you may be able to avoid or lower the penalty by annualizing your income and making unequal payments. Use Form 2220, Underpayment of Estimated Tax by Corporations .
This is the IRS’s own guidance reproduced from the IRS notice page. It describes the IRS’s process — it is not legal or tax advice from TaxRiskOS.
Governing IRS procedure (Internal Revenue Manual)
The IRS’s own internal procedures for handling this notice type are documented in the Internal Revenue Manual:
Reference to published IRS procedure. General information — not legal or tax advice.
Official IRS reference
Read the official notice page on IRS.gov: https://www.irs.gov/individuals/understanding-your-cp173-notice
Related tools
TaxRiskOS is workflow software for practitioners — it captures the notice, computes the deadline, surfaces the escalation tier, and builds a document checklist. It documents process; it does not give advice or draft responses.
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