Interest under section 234C applies to presumptive taxpayers where advance tax shortfall attracts a short fixed-period simple interest charge. For assessees opting for presumptive taxation, interest under the delayed-advance-tax provision is charged when advance tax paid by the prescribed cutoff is less than assessed tax; the shortfall equals assessed tax minus tax deposited by the prescribed date and simple interest at the statutory short-period rate is imposed for the single prescribed short period on that shortfall.