Sec 660 !new! ◎

For modern practice, always cite for interest on underpayments. However, when researching a case from the 1970s or earlier, the original Section 660 is the controlling authority.

The IRS generally has three years from the filing date to assess a deficiency. If they invoke SEC 660 on a return that is eight years old, and you did not sign a waiver (Form 872), the penalty may be time-barred.

This compounding effect is a direct legislative modification of the original simple-interest Section 660. sec 660

To understand the severity of SEC 660, you must understand the normal penalty landscape:

If the IRS admitted that your extension request was not abusive—for example, you filed an extension because you were waiting for a K-1 from a partnership—SEC 660 fails. The delay must be part of the negligence/fraud . For modern practice, always cite for interest on

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. This has historically limited how the US Department of State and USAID interact with international law enforcement agencies. 16 CFR Part 660 (FCRA) : These are federal regulations concerning the Accuracy and Integrity of Information If they invoke SEC 660 on a return

When the Internal Revenue Service (IRS) believes a taxpayer has underpaid their taxes, the standard procedure is to assess the tax, add interest, and possibly add a failure-to-pay penalty. However, when the IRS suspects the taxpayer is intentionally dragging their feet, hiding assets, or engaging in “dilatory tactics,” they reach for a far more powerful tool:

Let’s clear up a common confusion first. Many people confuse SEC 660 with the more famous (interest on underpayments) or § 6651 (failure to file/pay penalties). SEC 660 is distinct.

Disclaimer: This article is for informational purposes only and does not constitute legal or tax advice. IRS rules are complex and subject to change. Always consult with a qualified tax professional regarding your specific situation.

In current practice, much of the operational detail of Section 660 has been superseded or expanded by and Section 6621 . However, understanding Section 660 in its original and amended form is crucial for tax professionals dealing with older tax years, audits extending back decades, or computational rules for interest accrual.