As regards financial creditors, the IRP/RP should take into account the interest claimed as per the terms of the loan agreement including penal interest, if any upto the insolvency commencement date.
For operational creditors, ordinarily the interest is not considered unless it is claimed by the operational creditor or other creditor and it is stated in purchase or work order. In other words, claim will be admitted to the extent there was agreement between the parties to charge and pay interest. If there is no agreement, merely the fact that it is mentioned in the invoice does not entitle the operational creditor to that interest. Interest has to be taken into account excluding the credit period as per the agreement or customary practice of the trade or usage having the force of law.
To conclude, no thumb rule can be established for providing and calculating the interest in claims by operational and other creditors; it depends on the facts and circumstances of each case.
Disclaimer: The views expressed here are views based on my personal interpretation for academic purposes alone and should not be deemed as legal or professional advise on the subject. If relied upon, the author does not take any responsibility for any liability or non-compliance.