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GST calculator — add or remove GST, with the CGST/SGST split

Two sums get called “calculating GST” and they are not the same. Adding 18% to ₹1,000 gives ₹1,180. Backing 18% out of ₹1,180 gives ₹1,000 — but subtracting 18% from ₹1,180 gives ₹967.60, which is wrong by ₹32.40 and is the single most common mistake on a hand-written bill.

By Khatamel · · Free, no account

This amount is
GST rate
Sale
Amount before GST
₹1,000.00
CGST at 9%
₹90.00
SGST at 9%
₹90.00
Total GST
₹180.00
Total payable₹1,180.00

Adding GST and taking it out are different sums

If your price is exclusive — the figure before tax — the tax is that figure times the rate. ₹1,000 at 18% is ₹180, and the invoice total is ₹1,180.

If your price is inclusive — the figure the customer actually pays — the base is the total times 100 divided by (100 + the rate). ₹1,180 at 18% gives a base of ₹1,000 and tax of ₹180. Subtracting the rate from the total instead is what produces ₹967.60: you would be taking 18% of the larger number.

A shop that quotes “all-inclusive” prices is in the second case every single time, which is why this calculator asks which one you mean before it answers.

CGST, SGST and IGST — which one goes on the bill

The rate does not change with the state; the split does. When the seller and the buyer are in the same state, the tax is halved into CGST and SGST — ₹180 becomes ₹90 and ₹90. When they are in different states it is one line of IGST at the full ₹180.

  • Same state (intra-state): CGST + SGST, half each.
  • Different states (inter-state): IGST, the whole amount on one line.
  • The total the customer pays is identical either way — only the lines differ.

Getting the split wrong does not change what you collect, but it does change what you file, and it is a correction somebody has to make later.

Where the odd paisa goes

Half of an odd number of paise is not a whole paisa. On ₹25 at 0.25% the tax is 6.25 paise, which rounds to 6, and 6 does not halve evenly either. The convention used here is to give the extra paisa to CGST, so the two halves still add back to the tax exactly.

It is one paisa. It matters because a bill where the parts do not add up to the whole is a bill somebody will query, and answering that query costs more than the paisa.

What this does not do

It does not tell you which rate applies to what you sell. That depends on the HSN or SAC code for the goods or service, rates are revised from time to time, and the only safe source is the current official rate for your own code.

It is arithmetic, not tax advice, and it files nothing. If a figure here disagrees with your accountant, your accountant knows something about your case that a calculator does not.

Common questions

How do I remove GST from a price that already includes it?

Multiply the total by 100 and divide by (100 + the rate). At 18%, ₹1,180 × 100 ÷ 118 = ₹1,000 of base and ₹180 of tax. Do not subtract 18% from the total — that takes 18% of the wrong number and leaves you short.

Is the GST rate different for an inter-state sale?

No. The rate is the same; only the split changes. Within one state it is CGST plus SGST, half each. Between states it is a single IGST line for the full amount, and the customer pays the same total.

What is the formula for adding GST?

Tax = price × rate ÷ 100, and the total is the price plus that tax. ₹1,000 at 18% is ₹180 of tax and ₹1,180 in total.

Which GST rate should I use?

It depends on the HSN or SAC code for what you are selling, and the rates change from time to time. This page calculates whatever rate you give it; it cannot tell you which one is correct for your goods.

Does this calculator store what I type?

No. The arithmetic runs in your own browser, nothing is sent anywhere and nothing is saved. You can use it without an account.

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