Rule 37A: Complete Guide to 180-Day ITC Reversal

What is Rule 37A of CGST Rules?

Rule 37A of the Central Goods and Services Tax (CGST) Rules, 2017, requires you to reverse input tax credit (ITC) if you haven't paid your supplier within 180 days of the invoice date.

This rule was introduced to prevent businesses from claiming ITC and then never paying their suppliers — a common tax evasion tactic.

The 180-day ITC reversal rule (explained simply)

The rule in plain language:

If you claim ITC on a purchase invoice, you must pay your supplier within 180 days. If you don't, you must reverse (give back) the ITC you claimed.

Key points:

• 180 days = from the invoice date, not the receipt date
• Applies to all invoices where ITC has been claimed
• Reversal happens in the GSTR-3B for the month after the 180-day period expires
• If you pay later, you can re-claim the ITC

When does ITC need to be reversed?

Scenario 1: You haven't paid within 180 days

• Invoice date: April 1, 2026
• 180 days from: April 1, 2026 = September 28, 2026
• Reversal month: October 2026 GSTR-3B (filed by November 20, 2026)

Scenario 2: Partial payment

• Invoice amount: Rs 1,00,000 (ITC: Rs 18,000)
• Paid within 180 days: Rs 60,000
• Unpaid: Rs 40,000
• ITC to reverse: Rs 18,000 x (40,000 / 1,00,000) = Rs 7,200

Scenario 3: You pay after reversal

• Reversed ITC in October 2026: Rs 18,000
• Paid supplier in November 2026
• Re-claim in: November 2026 GSTR-3B

How to calculate the reversal amount

Formula:

ITC to reverse = Total ITC on invoice x (Unpaid amount / Total invoice amount)

Example:

• Invoice: Rs 1,18,000 (Rs 1,00,000 + Rs 18,000 GST)
• ITC claimed: Rs 18,000
• Amount paid within 180 days: Rs 70,000
• Amount unpaid: Rs 48,000
• ITC to reverse: 18,000 x (48,000 / 1,18,000) = Rs 7,322

How to track 180-day deadlines

Manual tracking (error-prone):

• Maintain an Excel sheet with invoice date, amount, payment date
• Calculate 180 days for each invoice
• Flag invoices approaching the deadline

Automatic tracking (recommended):

• Use our free GST reconciliation tool to identify invoices
• Most accounting software (Tally, Zoho) can flag old unpaid invoices
• The GST portal's GSTR-2B shows ITC that needs reversal under Rule 37A

Best practice:

1. Run a monthly aging report of unpaid purchase invoices
2. Flag invoices older than 150 days (gives you 30 days buffer)
3. Pay or reverse before the 180-day deadline

What happens if you don't reverse

Consequences of non-compliance:

Consequence	Detail
Interest	18% per annum on the reversed ITC
Notice	DRC-01C show-cause notice
Penalty	Up to 10% of tax amount (Section 122)
ITC blocked	Future ITC claims may be scrutinized

The GST department tracks this through GSTR-2B and data analytics. If you claim ITC but don't reverse it after 180 days, the system will flag it.

Rule 37A vs Section 16(4) — what's the difference?

Feature	Rule 37A	Section 16(4)
What	Reverse ITC if not paid in 180 days	Deadline to claim ITC
Deadline	180 days from invoice date	November 30 of following FY
Reversible?	Yes — re-claim if you pay later	No — permanent loss after deadline
Trigger	Non-payment to supplier	Time passage
Where in GSTR-3B	Table 4(B)(1)	N/A (can't claim at all)

Both can apply:

• If you don't pay within 180 days -> reverse under Rule 37A
• If you don't claim by November 30 of following FY -> permanent loss under Section 16(4)

How to reverse ITC under Rule 37A in GSTR-3B

1. Calculate the total ITC to reverse for the month
2. In GSTR-3B, go to Table 4(B)(1) — "Ineligible ITC"
3. Enter the reversal amount
4. This reduces your net ITC for the month
5. Pay the additional tax (if any) + interest

How to re-claim ITC after payment

If you reversed ITC under Rule 37A and later pay the supplier:

1. The payment is reflected in your books
2. In the next GSTR-3B, add the re-claimed amount to Table 4(A) (eligible ITC)
3. The net effect is that you've re-claimed the previously reversed ITC

Important: You must re-claim before the Section 16(4) deadline (November 30 of the following financial year). After this, the ITC is permanently lost.

Common mistakes to avoid

1. Counting from receipt date, not invoice date — the 180 days start from the invoice date
2. Forgetting partial payments — you only reverse the proportionate ITC for the unpaid amount
3. Not tracking at all — many businesses don't track and get notices
4. Reversing the full amount instead of proportionate — only reverse for the unpaid portion
5. Missing the re-claim — if you pay later, remember to re-claim in the next GSTR-3B

Track your ITC deadlines with our free reconciliation tool.

**Rule 37A reversal formula:**

ITC to reverse = Total ITC x (Unpaid amount / Total invoice amount)

**Timeline:**
- Day 0: Invoice date
- Day 180: Deadline to pay supplier
- Day 181+: Reverse ITC in next GSTR-3B (Table 4(B)(1))

**Re-claim:** If paid later, re-claim in next GSTR-3B (Table 4(A))

**Interest:** 18% per annum on reversed ITC

**Section 16(4) deadline:** November 30 of following FY (permanent loss after this)