About this tool
What is GST?
Goods and Services Tax is India's unified indirect tax on the supply of goods and services, introduced in July 2017 to replace a patchwork of VAT, service tax, excise duty and a long list of cesses. It is a destination-based consumption tax: the revenue belongs to the state where the goods or services are consumed rather than where they were produced.
GST is charged at each stage of the supply chain, but registered businesses claim input tax credit for the GST they paid on their own purchases. The net effect is that tax is paid only on the value added at each step, and the final consumer bears the full amount.
GST slabs and how the tax splits
Most goods and services fall into one of five rates: 0%, 5%, 12%, 18% and 28%. Essentials such as unbranded food grains are exempt; 5% covers packaged staples and economy transport; 12% and 18% cover the bulk of manufactured goods and services; 28% applies to luxury and 'sin' categories, sometimes with an additional compensation cess.
The same total rate is split differently depending on where the buyer is.
- Intra-state supply — the rate is split equally into CGST (central) and SGST (state). An 18% invoice shows 9% CGST + 9% SGST.
- Inter-state supply — the full rate is charged as IGST and later apportioned between the centre and the destination state.
- Union territories — UTGST replaces SGST, with the same 50/50 split.
GST-exclusive vs GST-inclusive prices
This is where most manual calculations go wrong. If a price is exclusive of GST, the tax is added on top: GST amount = base × rate ÷ 100, and the total is base + GST. A ₹1,000 item at 18% becomes ₹1,180.
If a price is inclusive, the tax is already inside the number and must be extracted, not added: base = total × 100 ÷ (100 + rate). Working backwards from ₹1,180 at 18% gives a base of ₹1,000 and GST of ₹180. A common error is to take 18% of the inclusive figure (₹212.40), which overstates the tax by more than ₹32 on this invoice. The calculator handles both directions from a single field so you never have to remember which formula applies.
The formulas in full
Adding GST to a base price: GST = P × r ÷ 100, and Total = P × (1 + r ÷ 100).
Removing GST from an inclusive price: Base = T × 100 ÷ (100 + r), and GST = T − Base.
Splitting the tax for an intra-state invoice: CGST = SGST = GST ÷ 2. For inter-state supply the whole amount is IGST. Rounding is applied to the final invoice value, and most accounting systems round to the nearest rupee, which is why a hand calculation can differ by a paisa or two from your billing software.
Who needs this and what it is not
Freelancers raising invoices, small retailers checking a supplier bill, e-commerce sellers reverse-engineering a listing price, students learning the mechanics, and anyone who wants to know how much of a restaurant bill was actually tax — the calculator answers all of those in one step, with the CGST/SGST split shown alongside the total.
It is a calculation aid, not tax advice. Rates change through GST Council notifications, some categories carry a compensation cess, composition-scheme dealers work differently, and reverse-charge supplies shift liability to the buyer. For filing and compliance decisions, confirm the current rate for your HSN or SAC code and speak to a qualified professional.
Tips for best results
- 01Confirm whether the figure you have is inclusive or exclusive before you calculate — that single distinction causes most invoicing disputes.
- 02Look up the correct HSN (goods) or SAC (services) code for your product; the rate follows the code, not the industry.
- 03Use CGST + SGST for customers in your own state and IGST for customers outside it.
- 04Keep the base amount, tax amount and total as separate line items on every invoice — it makes input tax credit reconciliation far easier.
- 05Round only at the invoice total, not at each line, to avoid cumulative drift.
- 06Remember that some categories carry an extra compensation cess on top of the 28% slab.
- 07Save or screenshot the breakdown when quoting a client so both sides agree on what the tax component is.
Frequently asked questions
How do I remove GST from an inclusive price?+
Divide the total by (100 + rate) and multiply by 100. At 18%, a ₹1,180 total has a base of ₹1,000 and ₹180 of GST.
What is the difference between CGST, SGST and IGST?+
For sales within a state the rate splits equally into CGST and SGST. For sales across states the entire rate is charged as IGST.
Which GST rates does the calculator support?+
The standard slabs — 0%, 5%, 12%, 18% and 28% — plus any custom rate you type in.
Is the calculation done on my device?+
Yes. It is plain arithmetic in your browser; no amounts are sent anywhere or stored.
Does it account for compensation cess?+
No. Cess applies only to specific categories and varies by product, so add it separately after computing the base GST.
Is this tool free?+
Yes, completely free with no signup and no limits.
Can I use it for reverse-charge invoices?+
The arithmetic is identical, but under reverse charge the recipient pays the tax to the government instead of the supplier.