GST ITC Reversal Rules 42 & 43: Calculation Guide 2026

Every GST-registered business that sells a mix of taxable and exempt goods — or uses inputs partly for personal purposes — is legally required to reverse a portion of Input Tax Credit. Rules 42 and 43 of the CGST Rules, 2017 govern exactly how much you must give back. Miss this calculation, or get it wrong, and you face an 18% per annum interest charge on the under-reversed amount from 1 April of the following year — plus exposure to penalties under Section 122 of the CGST Act, 2017.

What makes Rules 42 and 43 particularly dangerous is that they look optional from the outside. Your GSTR-3B will accept a filing without the reversal. The demand only arrives during a GST audit or scrutiny assessment — often years later, when the interest bill has quietly compounded. This guide walks you through the complete calculation framework, with real rupee examples, so your business stays clean and your CA can defend every figure.

Why ITC Reversal Exists Under GST

GST is built on the principle that credit flows only through the productive chain of taxable commerce. When you use inputs to produce exempt goods — educational services, agricultural produce, healthcare — the GST paid on those inputs was never meant to flow as credit. The credit chain breaks the moment the output becomes tax-free. Similarly, when inputs are diverted for personal or non-business purposes, there is no justification for the government to subsidise them through the credit mechanism.

Section 17(1) and Section 17(2) of the CGST Act, 2017 establish this principle. Rules 42 and 43 of the CGST Rules, 2017 give you the precise formula to compute how much must be reversed each tax period.

Rule 42: ITC on Inputs and Input Services

Rule 42 applies to ITC on inputs (raw materials, consumables, trading goods) and input services (professional fees, logistics, software subscriptions, utilities) that serve both taxable and exempt supply activities, or that partly serve personal use.

The Five-Step Formula

Step 1 — Identify hard reversals

From your total ITC for the month (T), identify three categories that must be reversed in full:

• T1: ITC on goods and services used exclusively for non-business or personal purposes
• T2: ITC on goods and services used exclusively for exempt supplies
• T3: ITC blocked under Section 17(5) — motor vehicles, food and beverages, beauty treatment, club memberships, health services, and works contract services used for construction of immovable property

C1 = T1 + T2 + T3 — reverse completely, no partial credit possible

Step 2 — Ring-fence your safe credit

• T4: ITC on goods and services used exclusively for taxable supplies, including zero-rated exports under a Bond or LUT

This credit belongs entirely to your business. Protect it with clear invoice tagging in your accounting records.

Step 3 — Compute common credit

The residual after removing hard reversals and exclusively taxable credit:

C2 = T − T1 − T2 − T3 − T4

C2 represents inputs and services that benefit both taxable and exempt activities simultaneously — a shared resource that must be split proportionately.

Step 4 — Split the common credit

Two reversals apply to C2 every month:

• D1 = C2 × (Aggregate exempt turnover during the tax period ÷ Aggregate total turnover during the tax period)
• D2 = C2 × 5% — a flat proxy for non-business use of common resources

Step 5 — Net eligible ITC

Net ITC = T − C1 − D1 − D2

Add both D1 and D2 to your output tax liability in Table 4(B)(2) of GSTR-3B each month.

Worked Example: Rule 42 in Practice

Arjun Traders Pvt Ltd, a pharmaceutical distributor in Mumbai, reports April 2026 turnover of ₹1.2 crore — ₹90 lakh from taxable medicines and ₹30 lakh from exempt diagnostic kits (notified as exempt under GST).

Arjun Traders adds ₹2,22,500 to its GSTR-3B output liability in April. The ITC reduces from ₹12 lakh (claimed) to ₹9.77 lakh (eligible) — a reversal that, if skipped, would cost approximately ₹40,050 in annual interest alone (₹2,22,500 × 18%).

Annual Reconciliation Under Rule 42(2)

Monthly D1 calculations use monthly turnover ratios, which fluctuate with seasonal sales. Rule 42(2) requires a full-year recalculation once the financial year closes:

1. 1Sum all monthly T, T1, T2, T3, T4 figures for the full year
2. 2Recompute C1, C2, D1, D2 using annual turnover figures — not a monthly average
3. 3Compare the annual D1 + D2 total against the sum of all monthly reversals already reported in GSTR-3B

If the annual figure exceeds monthly reversals: pay the shortfall by adding it to Table 4(B)(2) of GSTR-3B in the month you complete the computation. Interest at 18% per annum runs from 1 April of the succeeding financial year — not from the month you file the correction. Delayed annual reconciliation directly increases interest exposure.

If the annual figure is less than monthly reversals: reclaim the excess in the same GSTR-3B by crediting Table 4(A)(5).

Rule 43: ITC on Capital Goods

Capital goods — manufacturing machinery, computers, servers, commercial vehicles, office furniture — provide economic benefit over several years. Rule 43 recognises this by spreading the ITC reversal across 60 months (5 years), regardless of your actual depreciation method under the Companies Act or Income Tax Act.

How the 60-Month Calculation Works

For each capital good, calculate once at purchase:

• Tm = Total ITC on the capital good ÷ 60 (fixed monthly eligible amount)

Each month thereafter:

• Monthly exempt ratio = Exempt turnover for the month ÷ Total turnover for the month
• Monthly reversal = Tm × exempt ratio
• Add this reversal to Table 4(B)(2) of GSTR-3B

The Tm value never changes across the 60 months. Only the exempt ratio moves month to month. If the capital good is exclusively for taxable supplies, no monthly reversal applies — Tm flows through as eligible ITC in full. If exclusively for exempt use, the ITC cannot be claimed at all: reverse it entirely at the time of purchase.

Worked Example: Rule 43

Renuka Fab Works, a Surat textile processor, installs a new warping machine in April 2026 at ₹50 lakh + 18% GST. The GST paid is ₹9,00,000, which is claimed as ITC. The machine processes both taxable polyester yarn (60% of output) and exempt khadi fabric (40%).

If production in June shifts to 30% exempt output, the June reversal drops to ₹15,000 × 30% = ₹4,500. The Tm holds at ₹15,000 for all 60 months — only the ratio changes. Over the full 60 months, Renuka Fab Works will reverse between ₹0 and ₹9,00,000 in total depending on how the exempt ratio moves each month.

Disposal Before 60 Months

If Renuka Fab Works sells the warping machine at month 24 for ₹30 lakh, Section 18(6) of the CGST Act requires reversing the higher of:

• Remaining Rule 43 eligible ITC: Tm × remaining months = ₹15,000 × 36 = ₹5,40,000
• GST on the sale transaction value: ₹30 lakh × 18% = ₹5,40,000

In this case, both amounts coincide. If the sale value were ₹32 lakh, the GST-based figure (₹5,76,000) would exceed the remaining ITC and become the reversal amount. Always compute both figures before closing a capital goods disposal transaction.

Reporting ITC Reversals in Returns

Table 7 of GSTR-9 aggregates all ITC reversals for the full year. Discrepancies between GSTR-3B totals and GSTR-9 Table 7 generate system-generated notices from the department — the most common trigger for scrutiny assessments under Section 61.

Five Mistakes That Trigger GST Demand Notices

No de minimis exemption. Rules 42 and 43 have no threshold below which the calculation is optional. Even if exempt sales are 2% of turnover and the reversal works out to ₹800 a month, the law requires it. A Section 61 scrutiny officer computing the full-year shortfall will assess interest from 1 April regardless of the amount involved.

Using income tax turnover in the denominator. The Rule 42 denominator is "aggregate turnover" under Section 2(6) of the CGST Act — which differs from the gross turnover reported in the income tax return. Substituting the wrong figure skews the exempt ratio and produces either under- or over-reversal, both of which create reconciliation problems at audit time.

Treating Rule 43 as a one-time entry. Many businesses reverse ITC on capital goods once at purchase and file nothing in subsequent months. The law requires a monthly entry for all 60 months. Fifty-nine months of missed reversals represent 59 separate assessable periods, each with interest running from 1 April of the relevant year.

Dumping all purchases into common credit. If your accounting software tags every purchase as common rather than taxable-only or exempt-only, C2 inflates unnecessarily. Freight for taxable-only goods, tooling for taxable-only production, professional fees for taxable-only projects — these belong in T4. Correct tagging at invoice entry reduces D1 directly and can save several lakh rupees annually for a mid-size manufacturer.

Skipping the annual reconciliation. Rule 42(2) mandates the year-end recomputation. If the shortfall is discovered during a department audit rather than through your own voluntary correction, interest accrues from 1 April of the year following the shortfall — not the audit date. Filing the annual adjustment before GSTR-9 is due contains the interest bill at the minimum legal exposure.

Key Takeaways

• Rule 42 covers inputs and input services: reverse C1 (T1+T2+T3) fully, then apply the D1 (exempt ratio) and D2 (5% flat) formula to common credit C2 each month.
• Rule 43 covers capital goods: divide total ITC by 60 and reverse the exempt-ratio portion every month for 60 months from the date of purchase.
• Both rules require an annual reconciliation; under-reversals attract 18% interest from 1 April of the succeeding financial year.
• Precise invoice tagging — marking each purchase as taxable-only, exempt-only, or common — is the single biggest lever to reduce D1 reversals and keep C2 lean.
• Reversals are reported in GSTR-3B Table 4(B) monthly and reconciled in GSTR-9 Table 7 annually.
• Selling a capital good before 60 months triggers Section 18(6): compare remaining ITC with GST on sale value, and reverse the higher amount.

How corpus Helps

Manual Rules 42 and 43 calculations across hundreds of purchase invoices, multiple supply streams, and month-by-month turnover fluctuations are where spreadsheets fail and tax exposure accumulates quietly. corpus automatically classifies each purchase invoice by supply type at the point of entry — taxable-only, exempt-only, or common — using your GST registration data and commodity codes. D1 and D2 are computed in real time for each return period, and GSTR-3B Table 4(B) is pre-filled with the correct reversal figures before your CA reviews the return.

For capital goods, corpus maintains an asset-level 60-month amortisation schedule. Each month, the system pulls your actual GSTN turnover data, updates the exempt ratio, and posts the Rule 43 reversal to the GSTR-3B automatically. When a capital good approaches 60 months or is flagged for disposal, corpus generates the Section 18(6) comparison — remaining ITC against GST on sale value — so the higher figure flows into the final return without manual calculation.

At year-end, the annual reconciliation report surfaces the variance between your monthly reversals and the annualised D1 + D2 position, giving your team time to file the adjustment before GSTR-9 is due rather than responding to a scrutiny notice months later.

If your business sells even one exempt product or service — unprocessed food, healthcare, education, agricultural inputs — Rules 42 and 43 are live obligations this month. Run the calculation, reconcile what may have been missed in prior months, and bring the annual position in order before October deadline season arrives.