Reverse GST Calculator

Reverse GST calculation extracts the GST portion from a price that already includes it. GST-inclusive = base value + GST, so the base value is Inclusive Amount × 100 / (100 + rate). This page does that arithmetic instantly, with a CGST/SGST or IGST breakdown.

Common cases: bought goods at MRP and need the taxable value for accounting, received an all-inclusive quotation, checking how much tax you paid on a restaurant bill, or reconciling expenses for input tax credit (ITC) claims.

The formula is identical for every slab; only the rate changes. At 18%, GST = amount × 18/118. At 5%, GST = amount × 5/105. Enter the correct slab for the product and the split happens automatically.

If the supply is intra-state (within one state), tax divides into equal CGST and SGST halves shown separately. If inter-state, the full tax is IGST. Toggle intra/inter-state in the calculator to see both.

Multiply the total by 18 and divide by 118. From an ₹11,800 GST-inclusive total: GST = 11,800 × 18 ÷ 118 = ₹1,800.00 and Base = ₹10,000.00. Intra-state, that GST splits as CGST ₹900 + SGST ₹900. The calculator does this for any amount and slab.

Base Value (net price) = Inclusive Amount × 100 ÷ (100 + GST rate), and GST Amount = Inclusive Amount − Base Value. At 5%: divide by 105 of the factor 100 — i.e. GST = Amount × 5/105. At 18%: Amount × 18/118. At 40%: Amount × 40/140.

MRPs are printed GST-inclusive. Apply Base = MRP × 100 ÷ (100 + rate) with the slab that applies to the item, then GST = MRP − Base. Example: an ₹5,900 MRP at 18% contains ₹900 of GST (5,900 × 18 ÷ 118) and a ₹5,000 base value.

At the 5% slab, GST = Total × 5 ÷ 105. A ₹1,050 GST-inclusive bill contains ₹50 of GST (1,050 × 5 ÷ 105 = 50), leaving a ₹1,000 base value. For intra-state bills the ₹50 splits as CGST ₹25 + SGST ₹25.

First extract the total GST with GST = Total × Rate ÷ (100 + Rate), then split it exactly in half. At the 18% slab from an ₹11,800 total: total GST ₹1,800 → CGST ₹900 + SGST ₹900 — each CGST/SGST half equals Total × 9 ÷ 118.

Enter the bill total and the rate the supplier used in the calculator, then compare the computed CGST/SGST/IGST figures with what the supplier printed. If they differ, the invoice is overstated or understated — reconcile before claiming input tax credit in GSTR-3B, because your credit must match what the supplier actually reported in GSTR-1.

Base value = Inclusive price × 100 ÷ (100 + rate). This is the taxable value you would report per invoice. Example: from an ₹23,600 GST-inclusive price at 18%, the base value is 23,600 × 100 ÷ 118 = ₹20,000.00.

Most standalone restaurants now charge 5% GST with no input tax credit (18% applies where credit is passed on, e.g. many in-house outlets). From a ₹1,050 restaurant bill at 5%: GST = 1,050 × 5 ÷ 105 = ₹50.00. If the bill shows separate service charges, add them to the taxable value first — they are taxed too.

Yes — the formula is the same for any rate; only the number changes. Enter 12% or 28% in the custom-rate field and the calculator extracts the tax exactly as the old invoice would have shown it, including the CGST/SGST halves (6% + 6% at 12%, 14% + 14% at 28%).

Because dividing by (100 + rate) almost never lands on a round base: 118, 105 and 140 do not divide most totals evenly. That is exactly why exact integer-arithmetic matters — this calculator rounds half-up at the paise level, so the extracted base value and GST add back perfectly to the total you entered, matching GSTR figures to the cent.