GST Calculator — CGST, SGST & IGST Calculator for B2B Invoices
Calculate GST instantly — add or extract GST from any amount, with automatic CGST+SGST/IGST split for intrastate and interstate B2B invoices.
Calculator
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Taxable (base) value: ₹100000.00
Total GST: ₹18000.00
CGST: ₹9000.00
SGST: ₹9000.00
Invoice total: ₹118000.00
Formula
GST-exclusive (add GST): GST Amount = Base Amount × Rate ÷ 100; Total = Base Amount + GST Amount. GST-inclusive (extract GST): GST Amount = Total × Rate ÷ (100 + Rate); Base Amount = Total − GST Amount. Intrastate split: CGST = SGST = GST Amount ÷ 2. Interstate: IGST = full GST Amount.
Example calculation
A vendor invoice of ₹1,00,000 (base) at 18% GST, intrastate supply: GST Amount = 1,00,000 × 18 ÷ 100 = ₹18,000, split as CGST ₹9,000 + SGST ₹9,000. Invoice total = ₹1,18,000. For an interstate supply of the same order, IGST = ₹18,000 (no CGST/SGST split), same total ₹1,18,000.
Engineering notes
Use CGST+SGST when the supplier and place of supply are in the same state; use IGST when they are in different states (or for imports/exports) — total GST liability is identical either way, only the split changes. The four standard slabs are 5%, 12%, 18%, 28%, with some goods/services outside GST or at special 0.25%/3% rates. For a B2B tax invoice, always show the base (taxable) value, GST rate, and tax amount as separate line items — never a single GST-inclusive lump sum — so the buyer can claim Input Tax Credit (ITC). When quoting or negotiating a contract price, confirm upfront whether the figure is GST-inclusive or exclusive; this calculator handles both directions.
When to use this calculator
- Preparing B2B tax invoices with correct CGST/SGST or IGST breakup
- Reverse-calculating the base price from a GST-inclusive quote received from a vendor
- Comparing vendor quotes on a like-for-like basis when one is GST-inclusive and another is exclusive
- Estimating landed cost of equipment or services before finalising a purchase order
Frequently asked questions
- How do I calculate GST on an amount?
- To add GST: GST Amount = Base Amount × GST Rate ÷ 100, then Total = Base Amount + GST Amount. Example: ₹50,000 at 18% GST = 50,000 × 18 ÷ 100 = ₹9,000 GST, so the total is ₹59,000.
- How do I remove/extract GST from a total (GST-inclusive) amount?
- GST Amount = Total × Rate ÷ (100 + Rate). Example: a ₹59,000 GST-inclusive invoice at 18% → GST = 59,000 × 18 ÷ 118 = ₹9,000, so the base (taxable) value is ₹50,000. Do not simply subtract the rate percentage from the total — that gives a wrong answer.
- What is the difference between CGST, SGST, and IGST?
- CGST (Central GST) and SGST (State GST) apply together, in equal halves, when the supplier and the place of supply are in the same state — e.g. 18% GST = 9% CGST + 9% SGST. IGST (Integrated GST) applies at the full rate when the supply crosses state lines, or for imports/exports. The total tax collected is the same either way; only how it is split between the central and state governments changes.
- What are the GST rate slabs in India?
- The standard GST slabs are 5%, 12%, 18%, and 28%, with a few special rates (0.25% and 3% on certain goods like precious stones/metals) and many essential goods/services exempt at 0%. Most industrial goods and B2B services commonly fall under 18% or 28% depending on HSN/SAC classification — always confirm the applicable rate against the current code.
- Do I need to show GST separately on a B2B tax invoice?
- Yes. Under GST invoicing rules, a tax invoice must show the taxable (base) value, the GST rate, and the tax amount (CGST+SGST or IGST) as separate line items — not folded into a single inclusive price. This is required for the buyer to claim Input Tax Credit (ITC) on the purchase.
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