GST Calculation Examples: Step-by-Step Guide
Five worked GST calculation examples spanning every common Indian invoice scenario — from small intra-state retail sales to inter-state B2B billing.
Refresher: the two GST formulas
Adding GST to a base price:
- GST = Base × Rate ÷ 100
- Final = Base + GST
Removing GST from a tax-inclusive price:
- Base = Final ÷ (1 + Rate ÷ 100)
- GST = Final − Base
Example 1: Small retail sale (intra-state, 5%)
A grocery store in Bangalore sells branded paneer worth ₹400 (base price). GST on packaged dairy products is 5%.
- GST: ₹400 × 5% = ₹20
- CGST (2.5%): ₹10 — goes to Centre
- SGST (2.5%): ₹10 — goes to Karnataka
- Final invoice: ₹420
Example 2: Restaurant bill (intra-state, 18%)
A diner in Delhi gets a bill of ₹2,360 inclusive of GST. The restaurant charges 18% (most non-AC restaurants charge 5%; we’re using 18% for the example).
- Base: ₹2,360 ÷ 1.18 = ₹2,000
- Total GST: ₹360
- CGST (9%): ₹180
- SGST (9%): ₹180
Example 3: B2B inter-state sale (18%)
A software company in Mumbai sells a ₹5 lakh enterprise license to a client in Hyderabad. Software services attract 18% GST.
- Base: ₹5,00,000
- IGST (18%): ₹90,000 — entirely to Centre, then shared with destination state (Telangana)
- Final invoice: ₹5,90,000
Notice the difference from intra-state: there is no CGST/SGST split, only IGST, even though the total tax is the same 18%.
Example 4: Reverse calculation — finding base from MRP
A customer wants to know how much GST is embedded in the MRP of a smartphone tagged at ₹14,160. Smartphones currently attract 18% GST.
- Base: ₹14,160 ÷ 1.18 = ₹12,000
- GST embedded: ₹2,160
This is the calculation every Indian buyer does mentally when comparing pre-GST to post-GST prices.
Example 5: Mixed-rate invoice
A bakery in Pune sells: bread (0% GST) ₹50, packaged biscuits (18%) ₹100, and a chocolate cake (28%) ₹500. Same buyer, single invoice.
- Bread: ₹50 × 0% = ₹0 GST
- Biscuits: ₹100 × 18% = ₹18 GST (CGST ₹9, SGST ₹9)
- Cake: ₹500 × 28% = ₹140 GST (CGST ₹70, SGST ₹70)
- Subtotal: ₹650 ; Total GST: ₹158 ; Invoice: ₹808
For multi-rate invoices, list each item separately on the invoice with its own GST rate and amount. Mixing them into one line breaks ITC reconciliation for the buyer.
Frequently asked questions
How do I round the GST amount?
GST law allows rounding to the nearest rupee at the invoice level (not per line item). Round half-up: ₹0.50 rounds up to ₹1, ₹0.49 rounds down to ₹0.
What if the buyer is in another country?
Exports of goods and services are zero-rated under GST. You charge 0% GST and can claim a refund on input taxes. Document with a tax invoice marked "EXPORT".
Do I need to charge GST as a freelancer?
Only if your annual turnover exceeds ₹20 lakh (₹10 lakh in some special-category states). Below that, GST registration is voluntary.
How does GST work for digital service exports?
Digital services to clients outside India are zero-rated exports. Charge 0% GST on the invoice but file as an export (with LUT or with bond). You can claim ITC refunds on inputs used to deliver these services. Common for Indian freelancers serving US, UK, or EU clients.
Can I issue a single invoice for multiple states?
No. If you have multiple delivery locations across states, the place of supply for each line determines the tax. Either issue separate invoices per state or include a state-wise breakdown on a single invoice with the correct CGST/SGST or IGST split for each line.
Related reading
- GST Rates Explained 2026
- GST for Small Business Owners
- Common GST Mistakes to Avoid
- Home Loan EMI Calculation
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