Reverse GST Calculator
Have a total with GST already in it? Enter it below to get the taxable value and the GST back, split into CGST/SGST or IGST. The formula is taxable value = total × 100 ÷ (100 + rate).
GST 2.0 (from 22 Sep 2025) uses 5%, 18% and 40%. For an older bill at 12% or 28%, type it into Custom %.
A folder of inclusive-priced bills to break up? Extract them all to Excel at once.
Convert to ExcelThe Reverse GST Formula
Forward GST is easy: take the taxable value, add the rate. Reverse GST is the one people get wrong, because the tax is already baked into the number in front of you and the rate does not apply to that number.
| What you want | Formula |
|---|---|
| Taxable value | Total × 100 ÷ (100 + rate) |
| GST amount | Total − Taxable value |
| CGST (intra-state) | GST amount ÷ 2 |
| SGST (intra-state) | GST amount ÷ 2 |
| IGST (inter-state) | GST amount (no split) |
The Mistake That Costs You Money
The instinct is to take 18% of the total. On a ₹11,800 bill that gives ₹2,124 of GST — and it is wrong by ₹324, every time.
The 18% was charged on ₹10,000, not on ₹11,800. Applying the rate to the tax-inclusive figure charges tax on the tax. Divide instead: 11,800 ÷ 1.18 = 10,000, so the GST is ₹1,800. The error grows with the rate — at 40% taking the rate off the top overstates the tax by nearly 29% of the correct figure. If you book the overstated number as input tax credit, that is a claim you cannot support and a reversal with interest waiting for you later.
Worked Examples at 18%
Common inclusive totals and what is actually inside them.
| Total (incl. GST) | Taxable value | GST @ 18% | CGST | SGST |
|---|---|---|---|---|
| ₹ 1,180 | ₹ 1,000.00 | ₹ 180.00 | ₹ 90.00 | ₹ 90.00 |
| ₹ 5,000 | ₹ 4,237.29 | ₹ 762.71 | ₹ 381.36 | ₹ 381.36 |
| ₹ 11,800 | ₹ 10,000.00 | ₹ 1,800.00 | ₹ 900.00 | ₹ 900.00 |
| ₹ 25,000 | ₹ 21,186.44 | ₹ 3,813.56 | ₹ 1,906.78 | ₹ 1,906.78 |
| ₹ 1,00,000 | ₹ 84,745.76 | ₹ 15,254.24 | ₹ 7,627.12 | ₹ 7,627.12 |
Notice that round inclusive totals almost never produce round taxable values. That is normal, and it is why an invoice raised from an inclusive price will show awkward paise in the taxable column.
Reverse GST at Each Slab
The divisor is simply 1 + rate. Under GST 2.0 (in force from 22 September 2025) the main slabs are 5%, 18% and 40%; the 12% and 28% divisors still matter for older bills and for credit notes issued against them.
| Rate | Divide the total by | GST as a share of the total |
|---|---|---|
| 5% | 1.05 | 4.762% |
| 12% (pre-GST 2.0) | 1.12 | 10.714% |
| 18% | 1.18 | 15.254% |
| 28% (pre-GST 2.0) | 1.28 | 21.875% |
| 40% | 1.40 | 28.571% |
When Compensation Cess Is In the Total
On sin and luxury goods — aerated drinks, tobacco, some cars — a compensation cess sits alongside GST, and both are charged on the same taxable value. So the divisor becomes 1 + GST rate + cess rate, not two separate reversals. A ₹1,000 total at 40% GST plus 12% cess reverses to 1,000 ÷ 1.52 = ₹657.89 taxable, ₹263.16 GST and ₹78.95 cess. Reversing the GST first and the cess afterwards gives the wrong answer, so use the combined divisor. The calculator above handles it if you fill the cess field.
Where This Comes Up
Reverse calculation is not an academic exercise — it is most of a day's bookkeeping in a business that buys at retail. Restaurant and hotel bills printed as a single figure. Cash memos with no tax break-up. MRP-inclusive purchases. Contracts quoted "all inclusive" where you must split the invoice yourself. Payment-gateway settlements that net everything into one line.
In every one of those cases you need the tax component separately, because input tax credit is claimed on the tax, never on the gross. Book the total and you have claimed nothing; book a guessed split and you have claimed something you cannot defend when it is matched against GSTR-2B.
Reverse GST vs Reverse Charge — Not the Same Thing
Two different ideas share a word. Reverse GST calculation is arithmetic: pulling the tax out of a total. Reverse charge mechanism (RCM) is a legal provision under Section 9(3) and 9(4) that moves the liability to pay tax from the supplier to the recipient for notified supplies — goods transport agency services, legal services, purchases from unregistered dealers, and so on. One is a formula; the other decides who pays the government. Under RCM you also pay at the normal rate and, if eligible, claim the credit back.
Related Tools & Guides
- GST Calculator — the forward direction: add GST to a taxable value
- GST Invoice Reader — pull taxable value and the CGST/SGST/IGST split out of a folder of PDFs into Excel
- GST Invoice Generator — raise a compliant invoice with the split calculated for you
- HSN Code Lookup — confirm which rate applies before you reverse anything
- CGST vs SGST vs IGST — which split belongs on your bill and why
- GST 2.0 on Your Invoice — why the same product shows 18% on an old bill and 5% on a new one
Breaking up a stack of inclusive-priced bills?
Drop the PDFs in and get taxable value, GST, and the CGST/SGST/IGST split in their own Excel columns — no reversing by hand, no rounding drift. Free to try, no signup.
Convert to ExcelFrequently Asked Questions
What is the formula for reverse GST calculation?
Taxable value = total amount × 100 ÷ (100 + GST rate), and GST amount = total − taxable value. For an 18% bill of ₹11,800 the taxable value is 11,800 × 100 ÷ 118 = ₹10,000 and the GST is ₹1,800. The common mistake is taking 18% of the total instead, which gives ₹2,124 — wrong by ₹324, because the rate applies to the value before tax, not after.
How do I remove 18% GST from a total amount?
Divide the total by 1.18. That is the taxable value; the remainder is the GST. So ₹5,900 ÷ 1.18 = ₹5,000 taxable and ₹900 GST. For 5% divide by 1.05, for 12% by 1.12, for 28% by 1.28, for the 40% slab by 1.40. If compensation cess applies, divide by (1 + GST rate + cess rate), because both sit on the same taxable value.
How is the reverse GST split into CGST and SGST?
Work out the total GST first, then halve it. On an intra-state supply GST is shared equally between CGST and SGST, so ₹1,800 becomes ₹900 CGST and ₹900 SGST. On an inter-state supply the whole ₹1,800 is IGST with no split. Which one applies depends on the place of supply, not on where the invoice was printed.
When do I actually need to reverse-calculate GST?
Whenever you hold a tax-inclusive figure and need the components: an MRP-inclusive retail bill, a restaurant or hotel receipt printed as one number, a cash memo with no break-up, an "all inclusive" contract, or a payment-gateway settlement. You need the split to book the purchase and to claim input tax credit — ITC is claimed on the tax component, never on the gross amount.
Is reverse GST the same as reverse charge (RCM)?
No. Reverse GST calculation is arithmetic — extracting tax already inside a total. Reverse charge mechanism is a legal provision under Section 9(3)/9(4) that shifts liability for paying the tax from supplier to recipient for notified supplies such as goods transport agency or legal services. One is a formula; the other decides who pays the government.