PaisaMatch Plus

GST ITC reversal calculator: supplier not paid in 180 days

A purchase bill is still unpaid 180 days after the invoice date — how much input tax credit has to be reversed, and by when should you pay to keep it? Enter one invoice and see the answer head by head, using the same rule as the desktop app’s “ITC 180-day check”.

All calculations happen in your browser — nothing is sent

Invoice date

Check as on

Invoice value (including GST)

Still unpaid to the supplier

GST on the invoice (the ITC you claimed)

Within the state (CGST + SGST) From another state (IGST)

CGST

SGST / UTGST

Cess (if any)

The 180-day rule in short

Under the second proviso to section 16(2) of the CGST Act and Rule 37, a buyer who has claimed input tax credit must pay the supplier the value of the supply and the tax on it within 180 days from the invoice date. If part of the bill is still unpaid after that, the ITC on the unpaid part has to be paid back (reversed), with interest under section 50. Once the supplier is paid, the reversed ITC can be claimed again.

How the amount is worked out

Proportionate, not all or nothing: ITC to reverse = ITC on the invoice × unpaid amount ÷ invoice value (including GST), separately for IGST, CGST, SGST and cess — GSTR-3B takes the reversal head by head.
Example: an invoice of ₹1,18,000 dated 1 March 2026 (₹1,00,000 + CGST ₹9,000 + SGST ₹9,000) with ₹59,000 still unpaid on 30 September 2026 is 213 days old. Half the bill is unpaid, so half the ITC goes back: CGST ₹4,500 and SGST ₹4,500.
Last date to pay: the invoice date plus 180 days. Paying in full by then means nothing is reversed.

When the reversal goes in

Rule 37 asks for it in the GSTR-3B for the tax period right after the one in which the 180 days end, along with interest under section 50. The interest depends on when the credit was used, so this calculator does not work it out — your CA confirms the period and the interest.

Bills this rule does not cover

Supplies on which the buyer pays tax under reverse charge.
Supplies without consideration listed in Schedule I — treated as paid.
Amounts the buyer paid on the supplier’s behalf that were added to the value under section 15(2)(b) — also treated as paid.

Checking every supplier at once

One invoice is easy. The hard part is finding every old unpaid bill across all suppliers. The PaisaMatch Plus desktop app reads BUSY’s Bills Payable (FIFO) report with the purchase register and lists the bills past 180 days with the ITC to reverse head by head, plus the bills that will cross the limit in the next 30 days — so they can be paid first.

What this calculator does not do

It does not work out interest under section 50 or pick the return period.
It cannot tell a reverse-charge or Schedule I bill from a normal one — leave those out.
It takes the unpaid amount as you enter it. When payments are not against a particular bill, BUSY’s FIFO report applies them to the oldest bill first.

Questions about the 180-day ITC rule

What is the 180-day rule for input tax credit?

Under the second proviso to section 16(2) of the CGST Act and Rule 37, a buyer must pay the supplier the value and the tax within 180 days of the invoice date. Otherwise the ITC on the unpaid part has to be reversed, with interest under section 50.

How much ITC is reversed if only part of the bill is unpaid?

Only the proportionate part: ITC on the invoice × unpaid amount ÷ invoice value, separately for IGST, CGST, SGST and cess.

Can reversed ITC be claimed again?

Yes. Once the supplier is paid, the reversed ITC can be claimed again.

Does the 180-day rule apply to reverse charge supplies?

No. Supplies taxed under reverse charge are outside the rule. So are Schedule I supplies without consideration, and amounts added to the value under section 15(2)(b).