The amount of interest determined under this paragraph with respect to a prior taxable year is the amount of interest which would have been imposed under section
6601 on the underpayment of tax for such year which would have resulted if the gain (which is treated as ordinary income by reason of subsection (a)(1)) had been included in gross income in the taxable years in which it accrued (determined by treating the income as accruing at a constant rate equal to the applicable Federal rate as in effect on the day the transaction closed). The period during which such interest shall accrue shall end on the due date (without extensions) for the return of tax imposed by this chapter for the taxable year in which such transaction closed.