GST Calculator (Add or Remove GST)
Add GST to a base amount, or work backwards from a GST-inclusive total to find the original price and the tax portion. Works for standard slabs — 5%, 12%, 18%, 28% — or any custom rate.
How to use this calculator
- Enter the amount — either a pre-tax price or a GST-inclusive total.
- Pick the GST rate that applies to the goods or service.
- Choose Add GST if your amount is before tax, or Remove GST to extract tax from an inclusive total.
- Press Calculate to see the base, the GST amount (with CGST/SGST split) and the total.
Formula used
Where r is the GST rate as a decimal (0.18 for 18%). A common mistake when removing GST is subtracting 18% of the total — the correct method divides by 1.18, because the tax was charged on the smaller base amount.
Example calculation
Add: a service billed at 10,000 + 18% GST → GST = 1,800, invoice total = 11,800 (CGST 900 + SGST 900).
Remove: a receipt shows 11,800 including 18% GST → base = 11,800 ÷ 1.18 = 10,000, GST portion = 1,800.
What is GST?
GST (Goods and Services Tax) is a value-added tax charged on most goods and services, used in India, Australia, Singapore, New Zealand, Canada and many other countries. In India, goods and services fall into rate slabs — commonly 5%, 12%, 18% and 28% — with 18% covering most services.
On invoices within a state, the tax is split equally between the central government (CGST) and the state (SGST); across states, it's charged as a single IGST. Businesses collect GST from customers and offset the GST they paid on inputs, so the tax ultimately falls on the end consumer.
Why use this calculator?
- Create accurate invoices instantly — base, tax and total with the CGST/SGST split ready to copy.
- Reverse-calculate GST from any receipt to see how much tax you actually paid.
- Avoid the classic reverse-GST mistake of subtracting the percentage from the total.
Frequently asked questions
How do I remove GST from a total amount?
Divide the inclusive total by (1 + rate). For 18% GST: base = total ÷ 1.18. Example: 11,800 ÷ 1.18 = 10,000 base, so GST was 1,800. Never subtract 18% of the total — that gives the wrong answer.
What is the difference between CGST, SGST and IGST?
For sales within a state, GST is split equally: half CGST (central) and half SGST (state) — so an 18% tax is 9% + 9%. For sales between states, the full 18% is charged as IGST, collected by the centre and shared with the destination state.
What items fall under each GST slab in India?
Broadly: essential items are exempt or 5% (packaged food, transport), 12% covers processed foods and some goods, 18% is the standard rate for most services and manufactured goods, and 28% applies to luxury and sin goods like cars and tobacco. Rates change, so check the current schedule for specific items.
Does this calculator work for VAT in other countries?
Yes — the math for adding and removing any value-added tax is identical. Just select or treat the rate as your VAT rate (e.g. 20% UK VAT) and ignore the CGST/SGST split, which is specific to India.