Interest for defaults in furnishing return may accrue from differing start dates, altering the interest period and liabilities.
Section 423 charges simple interest for defaults in furnishing returns by applying a formula based on a tax base "A" and a period "T", with a Table linking specific filing or non-filing scenarios to starting and ending events for the interest period, reductions of the tax base by a prescribed definition of "tax paid", and provisions for adjustment (notice of demand or refund) where post-assessment orders change the tax on which interest is calculated.