Think of Section 50 as GST's late fee on the tax itself — separate from the late fee under Section 47 (which covers late filing). If you owe GST and don't pay it on time, the government charges you interest automatically, and the law expects you to calculate and pay it on your own — no demand notice required.
The basic rule (sub-section 1 & 2): Interest runs at 18% per annum (the currently notified rate) on the unpaid tax, starting from the day after the due date of payment until the actual date of payment. So if your GST for March was due on 20 April and you paid on 30 April, you owe 10 days of interest. Simple.
Here's the exam-critical twist — the 2021 proviso changed the base on which interest is charged. Earlier, interest was on the gross tax liability. Now, when you file a late return (but before any proceedings under Section 73 or 74 are initiated), interest is charged only on the net cash portion — meaning only the tax you pay by debiting your electronic cash ledger, NOT the portion covered by your Input Tax Credit (ITC) balance. This is a major relief for taxpayers who have ITC sitting in their ledger. However, if you file only after the department issues a notice under Section 73/74, this relief is gone — interest hits the full gross liability.
Excess ITC claims (sub-section 3): If you claim more ITC than you're entitled to, or you wrongly reduce your output tax liability, the interest rate jumps to 24% per annum. This is a penal rate, and it signals how seriously GST law treats ITC fraud or errors. This is asked frequently as a 4-mark question — examiners love pairing 18% vs. 24% in a scenario-based question.
📊 Worked example
Example 1 — Late filing, net cash interest (Proviso applies)
Rajesh & Co. Pvt. Ltd. has the following for the tax period March 2025:
- Output tax liability: ₹2,00,000
- ITC available in electronic credit ledger: ₹1,50,000
- Tax paid via electronic cash ledger: ₹50,000
- Due date for payment: 20 April 2025
- Actual date of return filing & payment: 5 May 2025 (no notice issued under Sec 73/74)
Working:
Delay = 20 April to 5 May = 15 days
Since return is filed late but before any Section 73/74 proceeding, interest applies only on the cash portion.
Interest = ₹50,000 × 18% × 15/365
Interest = ₹50,000 × 0.18 × 0.04110
= ₹369.86 ≈ ₹370
Final Answer: Interest payable = ₹370
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Example 2 — Excess ITC claim (24% rate)
Ms. Iyer wrongly claimed ITC of ₹80,000 in October 2024 that she was not entitled to. This was discovered and reversed on 1 February 2025. Due date for October return was 20 November 2024.
Working:
Period of excess claim = 21 November 2024 to 1 February 2025 = 73 days
Interest = ₹80,000 × 24% × 73/365
= ₹80,000 × 0.24 × 0.2
= ₹3,840
Final Answer: Interest @ 24% = ₹3,840
⚠️ Common exam mistakes
- Students apply 18% on gross liability ignoring the proviso. If the return is filed late but before Section 73/74 proceedings, interest is only on the cash ledger portion — not the full output tax. Always check whether ITC covers part of the liability.
- Students forget that 24% applies to excess ITC, not just late payment. 18% is for delayed payment of tax; 24% is reserved for undue/excess ITC claims or undue reduction of output tax under Sections 42/43. Don't mix them up in a scenario question.
- Students start counting interest from the due date itself. Sub-section (2) clearly says interest starts from the day succeeding (i.e., the day after) the due date. Always add 1 day before counting.
- Students assume interest is waived if the taxpayer files before receiving a notice. The proviso only changes the base (cash vs. gross). Interest itself is still payable — you don't get a full waiver just because no notice was issued.
- Students treat Section 50 interest and Section 47 late fee as the same thing. Section 47 = late fee for not filing the return on time (flat ₹50/day or ₹20/day). Section 50 = interest on the unpaid tax amount. Both can apply simultaneously.
📖 Bare Act text — Section 50, CGST Act 2017
(click to expand)
(1) Every person who is liable to pay tax in accordance with the provisions of this Act or the rules made thereunder, but fails to pay the tax or any part thereof to the Government within the period prescribed, shall for the period for which the tax or any part thereof remains unpaid, pay, on his own, interest at such rate, not exceeding eighteen per cent., as may be notified by the Government on the recommendations of the Council:
[Provided that the interest on tax payable in respect of supplies made during a tax period and declared in the return for the said period furnished after the due date in accordance with the provisions of section 39, except where such return is furnished after commencement of any proceedings under section 73 or section 74 in respect of the said period, shall be levied on that portion of the tax that is paid by debiting the electronic cash ledger.]
(2) The interest under sub-section (1) shall be calculated, in such manner as may be prescribed, from the day succeeding the day on which such tax was due to be paid.
(3) A taxable person who makes an undue or excess claim of input tax credit under sub-section (10) of section 42 or undue or excess reduction in output tax liability under sub-section (10) of section 43, shall pay interest on such undue or excess claim or on such undue or excess reduction, as the case may be, at such rate not exceeding twenty-four per cent., as may be notified by the Government on the recommendations of the Council.
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