Gst interest and penalty doubts regarding missing bills

Yes — interest will apply on the delayed payment of ₹36,000 liability, but penalty is not automatic. Late fees and penalties depend on whether you missed filing the GST return itself or only missed reporting those bills. Input tax credit (ITC) of ₹2 lakhs cannot offset interest liability; it only reduces net tax payable.

Interest under GST
•     Interest is charged under Section 50 of the CGST Act.
•     Rate: 18% per annum on the net tax liability (after ITC adjustment) that was not paid on time.
•     In your case, if ₹36,000 was missed in May 2025, interest accrues from the due date of GSTR-3B (20th June 2025) until the date you actually pay it.
•     Penalty vs. Late Fee
•     Late Fee: Applicable if you missed filing the return itself. Standard late fee is ₹50 per day (₹25 CGST + ₹25 SGST), capped at ₹5,000 for each return.
•     Penalty: Generally imposed only if there is fraud, suppression, or deliberate misstatement. For genuine omission of bills, penalty is not automatic.
•     If you filed GSTR-3B but missed reporting two invoices, you can amend/adjust in subsequent returns. No late fee arises, but interest on the missed liability does.

Input Tax Credit (ITC)
  Your available ITC of ₹2 lakhs can be used to offset the ₹36,000 liability.
  However, interest is calculated on the gross liability not discharged on time, even if ITC balance was sufficient. 

So sir even in may month period if I had excess input.. then also i should pay interest?

Yes, as the declaration is missed.