GSTINAPI

Reverse GST Calculator

Enter a price that already includes GST and get the base amount and the tax hidden inside it. Pick a rate and the split updates as you type.

The total you paid or were invoiced, tax included.

₹
GST rate charged
%

Base amount

Price before GST

GST inside

At

Total

What you entered

CGST

SGST

IGST

CGST and SGST apply when the supplier and the place of supply are in the same state; IGST applies when they are not. The total tax is identical either way — only the split changes.

Need to go the other way and add GST to a price? Use the GST calculator.

The reverse GST formula

Removing GST from a price is not the same operation as adding it, and the difference is where most mistakes happen. GST was charged as a percentage of the base, so to get back to the base you divide rather than subtract a percentage.

Base amount

base = inclusive × 100 ÷ (100 + rate)

GST component

gst = inclusive − base

At 18% the divisor is 118, so dividing by 1.18 gets you there in one step. On ₹10,000.00 including 18% GST the base is ₹8,474.58 and the GST inside it is ₹1,525.42.

₹10,000.00 inclusive, at every rate

The same inclusive amount worked backwards at each GST rate, with the wrong answer shown alongside so the size of the error is visible.

Rate Base amount GST inside CGST / SGST If you wrongly took % of the total
5% ₹9,523.81 ₹476.19 ₹238.10 each ₹500.00 (over by ₹23.81)
12% ₹8,928.57 ₹1,071.43 ₹535.71 each ₹1,200.00 (over by ₹128.57)
18% ₹8,474.58 ₹1,525.42 ₹762.71 each ₹1,800.00 (over by ₹274.58)
28% ₹7,812.50 ₹2,187.50 ₹1,093.75 each ₹2,800.00 (over by ₹612.50)
40% ₹7,142.86 ₹2,857.14 ₹1,428.57 each ₹4,000.00 (over by ₹1,142.86)
CGST and SGST are each half of the GST column on an intra-state supply. On an inter-state supply the whole GST amount is IGST.

Rates follow the GST 2.0 structure in force for FY 2026-27. Which rate applies to a given product or service is fixed per HSN or SAC code by notification — the full picture is in GST rate slabs in 2026.

When you need to work backwards

An MRP or a shelf price

Maximum retail price is tax-inclusive by law. To know what the goods actually cost before tax — for margin working, or to check a retailer is not adding GST on top of an MRP — you have to reverse it out.

A receipt that shows only a total

Restaurant and retail bills often print one figure. To claim input tax credit you need the tax component stated separately — and if the supplier will not issue a tax invoice showing it, that is itself a signal worth checking.

Quoting a customer a round final price

If you want the customer to pay exactly ₹5,000 all-in, you cannot price the job at ₹5,000 and add GST. Reverse the target price to find the base to quote.

Reconciling a purchase register

Where a supplier's total does not break out tax, reversing it is how you check their figure against what appears in your GSTR-2B — and mismatches there are the ones that cost credit.

Worth pairing with a check on the supplier itself: an invoice is only as good as the registration behind it. Look the GSTIN up to confirm the registration is active before you claim credit on it.

Reverse GST calculation — common questions

A reverse GST calculator works backwards from a GST-inclusive price to tell you the base amount and the tax hidden inside it. A normal GST calculator starts from a price before tax and adds GST on top; a reverse calculator starts from the total you actually paid and pulls the GST back out of it.
Base amount = GST-inclusive amount × 100 ÷ (100 + rate). The GST component is then the inclusive amount minus that base. On ₹10,000 including 18% GST the base is ₹10,000 × 100 ÷ 118 = ₹8,474.58, so the GST inside it is ₹1,525.42.
Divide the total by 1.18 to get the base, then subtract the base from the total to get the GST. On a ₹10,000 inclusive invoice the base is ₹8,474.58 and the GST is ₹1,525.42. Dividing by 1.18 and multiplying by 100 ÷ 118 are the same operation written two ways.
Because the 18% was charged on the base, not on the total. Taking 18% of a ₹10,000 inclusive price gives ₹1,800, but the GST actually embedded in it is ₹1,525.42 — an overstatement of ₹274.58. This is the single most common error in reverse GST calculation, and on input tax credit it means claiming more than the invoice supports.
Exactly as it is on a forward one. Once you have the total GST, an intra-state supply splits it evenly into CGST and SGST — half each. On ₹1,525.42 of GST that is ₹762.71 of CGST and ₹762.71 of SGST. An inter-state supply carries the whole amount as IGST with no split.
No, and the similar names cause real confusion. Reverse calculation is arithmetic — extracting the tax from a tax-inclusive figure. The reverse charge mechanism is a legal rule about who remits the tax: the supplier issues an invoice without GST and the registered recipient pays it directly to the government. The arithmetic on this page is unchanged under reverse charge; only the person who hands the money over changes.
Yes. Maximum retail price is a tax-inclusive figure by law, so the GST is already inside the number printed on the pack. That is precisely the case a reverse calculation is for — to find out how much of an MRP is tax and how much is the price of the goods.

Check the GSTIN on that invoice

Getting the tax split right does not help if the registration behind the invoice was cancelled. Verify any GSTIN against live government records — status, legal name and return filing history.

Look up a GST number Add GST instead