Sec 660 Better File

In current practice, much of the operational detail of Section 660 has been superseded or expanded by and Section 6621 .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.

A wealthy taxpayer files for an automatic extension (Form 4868) but knows they have a massive underpayment. They use the six-month grace period to invest the tax money, earning interest. When the IRS discovers the underpayment, they invoke SEC 660 to deny the benefit of the extension. sec 660