GST & Indirect Tax

GST 180-Day ITC Reversal Calculator: Rule 37 Working

CA Nikhil Gupta·Aug 2026·4 min readGST & Indirect Tax

Where a recipient fails to pay the supplier the value of supply plus tax within 180 days from the invoice date, proportionate ITC may need to be reversed…

Where a recipient fails to pay the supplier the value of supply plus tax within 180 days from the invoice date, proportionate ITC may need to be reversed with interest under section 16(2) and Rule 37, subject to exclusions such as reverse-charge supplies and deemed-payment situations.

Legal or Computational Framework

GST is levied on supply, not income. The second proviso to section 16(2) links ITC retention to payment of consideration and tax within 180 days. Rule 37 prescribes the reversal mechanism. For partial payment, reversal should be proportionate. Interest is computed under the current statutory rule from the prescribed starting point until reversal/payment, and the calculator must use the legally effective rate and period. Credit can generally be re-availed after payment to the supplier, subject to the rule. Reverse-charge supplies are outside this 180-day payment condition.

Step-by-step method

  1. Identify the correct tax period, taxpayer category and statutory provision.
  2. Reconcile source records before using any calculator.
  3. Compute each legal component separately rather than using a single unexplained output.
  4. Check current official notifications, extensions and portal validations.
  5. Preserve the calculation and supporting documents.

Worked Example

Invoice value is ₹1,00,000 plus GST of ₹18,000. The recipient pays ₹59,000, representing half the gross invoice, within 180 days and leaves half unpaid. Subject to allocation and Rule 37, ₹9,000 ITC may require reversal. The calculator should separately show ITC reversed, interest period and later re-availment after payment.

What Generic Pages Miss

  • Calculating 180 days from booking date instead of invoice date.
  • Reversing all ITC after partial payment.
  • Applying the rule to reverse-charge tax.
  • Ignoring interest.
  • Treating a bookkeeping credit note as supplier payment.

Practical Documentation Checklist

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Finin2min Summary

Where a recipient fails to pay the supplier the value of supply plus tax within 180 days from the invoice date, proportionate ITC may need to be reversed with interest under section 16(2) and Rule 37, subject to exclusions such as reverse-charge supplies and deemed-payment situations.

Frequently Asked Questions

Is GST charged on income?
No. GST is a tax on taxable supplies; income is an accounting or direct-tax concept.
When does the 180-day period start?
It is counted from the invoice date under the statutory condition.
What happens on partial payment?
The reversal is generally proportionate to the unpaid amount.
Does reverse charge follow this rule?
The 180-day payment condition does not apply to supplies on which tax is payable under reverse charge.
Can reversed ITC be reclaimed?
It can generally be re-availed after payment to the supplier, subject to Rule 37.
Should interest be calculated automatically?
Yes, but the tool must use the rate and start/end dates legally effective for the period.

Source and review trail

Use the current official instrument, portal or regulator publication before acting. This panel separates the category authority from page-specific references.

Primary category
GST & Indirect Tax
Official starting point
www.incometax.gov.in
Editorial review date
2026-08-02
Content status
Finin2min explanation; official source controls where facts, law, rates, forms or procedures can change.

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