GST Calculation Guide for India — Add, Remove & Split Tax

Goods and Services Tax (GST) unified many indirect taxes in India. Businesses and consumers still need to calculate tax on invoices, reverse tax from gross prices and split CGST/SGST or IGST correctly.

Adding GST to a base amount

Tax = Base × (Rate ÷ 100)

Gross = Base + Tax

Example: ₹1,000 + 18% GST → Tax ₹180 → Gross ₹1,180

Removing GST from a gross amount

When the price already includes GST:

Net = Gross ÷ (1 + Rate/100)

Tax = Gross − Net

Example: ₹1,180 inclusive at 18% → Net ₹1,000, Tax ₹180

CGST, SGST and IGST

Supply type	Split
Intra-state	CGST + SGST (each half of total GST)
Inter-state	IGST (full GST amount)

Example at 18% intra-state on ₹1,000 tax: CGST ₹90 + SGST ₹90.

Common GST slabs in India

• 5% — essentials, some food items
• 12% — processed foods, some services
• 18% — majority of goods and services
• 28% — luxury and sin goods (with cess on some items)

Always verify the applicable slab for your product or service.

Invoice checklist

1. State whether price is exclusive or inclusive of GST.
2. Show rate, tax amount and HSN/SAC where required.
3. Apply correct split for intra- vs inter-state supply.
4. Round per your accounting policy.

Free GST calculator

MerQPrime’s GST calculator adds or removes GST, supports all standard slabs plus custom rates, and shows CGST/SGST/IGST breakdown — instant and private.

After invoicing, let customers pay via UPI using a UPI QR code on the printed bill. Generate professional PDF invoices with the invoice generator, then add your QR image for faster collections.