TDS deducted not paid or TDS not deducted and not paid within the due date is to be equally penalised as regards interest. Because from the Govt. point of view they didnot received any revenue in both the case.
So, Interest would be calculated from the deductible date to the date of payment at 1.5% pm or partthere of. And in this case Interest would be calucated for three month if deductibe in NOv and paid in January or for two months if paid in December.
I hope it is clear now.