ITC Reversal Under Rule 42 & 43: A Complete Guide for CA Firms 2026

What Is ITC Reversal and Why It Matters

Under GST, Input Tax Credit (ITC) is the backbone of the tax system, allowing registered businesses to offset the tax paid on inputs against their output tax liability. However, not all ITC claimed can be retained — the GST law mandates reversal of credit in specific situations to prevent misuse.

Rules 42 and 43 of the CGST Rules, 2017 govern the reversal of ITC on inputs, input services, and capital goods used for both taxable and exempt supplies. For CA firms managing clients across sectors — real estate, hospitality, banking, insurance — these rules are among the most frequently triggered compliance obligations.

Failing to compute and reverse ITC correctly can lead to notices under Section 73/74, demand of tax with interest at 18% per annum, and penalties up to 100% of the tax due.

Understanding Rule 42: Inputs and Input Services

Rule 42 applies when a business uses inputs or input services partly for taxable supplies and partly for exempt supplies or non-business purposes.

The Formula

The reversal amount is calculated as D1 + D2 + D3, where:

• D1 = ITC attributable to non-business use = 5% of common ITC (C2)
• D2 = ITC attributable to exempt supplies = (Exempt turnover / Total turnover) × (C2 − D1)
• D3 = Final adjustment after reconciling with actual exempt supplies at year-end

Step-by-step monthly process:

1. 1Identify total ITC availed in the tax period (T)
2. 2Segregate ITC exclusively used for taxable supplies (T1), exempt supplies (T2), and non-business purposes (T3)
3. 3Compute common ITC: C1 = T − T1 − T2 − T3
4. 4Remove blocked ITC under Section 17(5) to arrive at C2
5. 5Apply D1 and D2 formulae to compute the reversal amount
6. 6Report in Table 4(B)(1) of GSTR-3B each month

Practical Example

A hospitality company in Mumbai has monthly ITC of ₹5,00,000. Breakdown:

• ₹1,50,000 exclusively for taxable restaurant services
• ₹50,000 blocked under Section 17(5) (employee accommodation)
• ₹3,00,000 is common ITC (C2)

Exempt turnover (accommodation under ₹1,000 per day): ₹8,00,000; Total turnover: ₹20,00,000

• D1 = 5% × ₹3,00,000 = ₹15,000
• D2 = (8/20) × (₹3,00,000 − ₹15,000) = 40% × ₹2,85,000 = ₹1,14,000
• Total monthly reversal = ₹1,29,000

This amount is reversed each month and reconciled at year-end using final annual turnover figures.

Understanding Rule 43: Capital Goods

Rule 43 deals with ITC on capital goods used for both taxable and exempt purposes. The treatment differs from Rule 42 in one key way: capital goods ITC is amortised over their useful life.

Key Points

• ITC on capital goods used exclusively for exempt supplies must be reversed immediately
• ITC on capital goods used exclusively for taxable supplies is retained in full
• For common capital goods, ITC is spread over 60 months (assumed useful life)
• Monthly reversal = (Exempt turnover / Total turnover) × (Total ITC on capital goods ÷ 60)

Practical Example

A manufacturer in Pune avails ITC of ₹6,00,000 on a machine used for both taxable and exempt goods.

Monthly ITC attributable to this machine = ₹6,00,000 ÷ 60 = ₹10,000

If the exempt-to-total turnover ratio for the month is 30%:

• Monthly reversal under Rule 43 = 30% × ₹10,000 = ₹3,000

This entry is posted monthly and the full position is reconciled at the end of the financial year.

Year-End Reconciliation and Final Reversal

Both Rule 42 and Rule 43 mandate an annual reconciliation using final full-year turnover figures:

1. 1Compute the total reversal required for the year using actual annual exempt and total turnover
2. 2Compare with the cumulative monthly reversals already made
3. 3If annual reversal required > sum of monthly reversals → pay the shortfall with interest u/s 50
4. 4If annual reversal required < sum of monthly reversals → claim the excess back as ITC in Table 4(A)(5) of GSTR-3B

The reconciliation must be completed in the GSTR-3B for September of the following financial year, or the date of filing GSTR-9, whichever is earlier.

Critical note: Interest u/s 50 runs from the date the excess ITC was originally availed — not from the date of discovery or filing. On ₹10,00,000 of excess ITC, even a 6-month delay attracts ₹90,000 in interest at 18% per annum.

Common Errors CA Firms Must Avoid

• Applying provisional turnover ratios — using estimated exempt turnover instead of actual monthly figures distorts D2 and compounds the year-end adjustment
• Omitting D1 (non-business use) — often missed in businesses where directors or partners use company vehicles or assets
• Not maintaining a capital goods register — without transaction-level tracking, Rule 43 computations become guesswork
• Missing the September deadline for annual reconciliation, which forfeits the right to reclaim any over-reversed ITC
• Wrong GSTR-3B table entry — Rule 42/43 reversals belong in Table 4(B)(1) and 4(B)(2), not Table 4(D), a mistake that triggers mismatches with GSTR-9

How corpus Helps

corpus automates ITC reversal calculations so your team spends zero time on spreadsheet gymnastics:

• Automatic turnover split — exempt and taxable turnover ratios are computed from your sales ledgers every month without manual input
• Rule 42 and Rule 43 dashboards — drill down from the D1/D2 summary to the individual transactions driving each figure
• Year-end reconciliation module — compares cumulative monthly reversals with the final annual computation and generates a ready-to-post GSTR-3B adjustment
• Interest exposure calculator — flags shortfalls before the September deadline so clients can act before interest accrues further
• Audit-ready trail — every computation is version-stamped, making GST audit responses straightforward

For CA firms serving clients in real estate, banking, or manufacturing — where exempt supplies are a routine part of the business — corpus turns a complex monthly compliance obligation into a one-click review.

Conclusion

ITC reversal under Rule 42 and Rule 43 is non-negotiable for any business with mixed-use inputs, services, or capital goods. The formulae are well-defined, but their correct application demands accurate turnover data, consistent monthly execution, and a disciplined year-end reconciliation.

Errors in ITC reversal attract not just tax demands but interest and penalties that can be multiples of the original credit. If your clients operate in sectors with significant exempt supplies, build Rule 42/43 into your standard monthly close checklist — or let corpus handle it automatically. Book a free demo to see how corpus manages ITC reversals end-to-end.