GST Calculator

Forwards and backwards

Adding GST is straightforward: the tax is the rate applied to your amount, and the total is the sum of the two. Extracting it from a total that already includes tax is where people go wrong, because subtracting the rate from the total does not work. On ₹11,800 at 18%, the base is the total multiplied by 100 and divided by 118 - that is ₹10,000, with ₹1,800 of tax. Subtracting 18% of ₹11,800 would give ₹9,676, which is wrong by over three hundred rupees.

Both directions round once, at the end, from the same unrounded intermediates. That is what makes them exact inverses of each other, which matters because a user who spots a rupee of disagreement between the two stops trusting the tool entirely.

Intra-state versus inter-state

Where the supplier and the recipient are in the same state, the tax splits equally into Central GST and State GST. Where they are in different states, it is a single Integrated GST at the full rate. The total is identical either way; what changes is which government receives it and how the recipient claims credit.

• Intra-state: CGST and SGST, half the rate each
• Inter-state: IGST at the full rate
• The total is the same in both cases
• The place of supply decides it, not where the invoice was raised

The slabs changed in September 2025

With effect from 22 September 2025 the GST Council collapsed the rate structure to two slabs, 5% and 18%, plus a 40% rate reserved for demerit, sin and super-luxury goods. The 12% and 28% slabs were abolished. Rates are set by Council meeting rather than by the annual Budget, so they move on their own schedule.

This page offers only the rates currently in force and prints the notification date alongside the result. Enter a superseded rate - to reconcile an older invoice, say - and it will compute it while telling you it is no longer a rate you can charge.

What it will not do

It will not tell you which rate applies to your goods or services. That is an HSN or SAC classification question with real consequences for getting it wrong, and it belongs to your accountant rather than to a calculator. We apply the mechanics to a rate you choose.

It also does not compute input tax credit, does not file returns, does not validate a GSTIN against the portal, and covers compensation cess only as a flat rate you supply - item-specific cess varies too much to model honestly.