Reverse GST Calculator
Enter a GST-inclusive price and get the price before GST, the GST amount and the CGST + SGST or IGST split. Free, instant and runs in your browser.
How to remove GST from a GST-inclusive price
If a price already includes GST, the amount before tax is the inclusive price divided by (1 + GST rate). The GST amount is the difference.
- Price before GST = inclusive price × 100 ÷ (100 + rate)
- GST amount = inclusive price − price before GST
- Example: ₹1,180 at 18% GST is ₹1,000 before GST plus ₹180 of GST
- Example: ₹10,500 at 5% GST is ₹10,000 before GST plus ₹500 of GST
Why you cannot just subtract 18% from the total
GST is charged on the price before tax, not on the total. Taking 18% off ₹1,180 gives ₹967.60, which is wrong. The correct pre-GST price is ₹1,000, because ₹180 is 18% of ₹1,000, not of ₹1,180.
CGST, SGST and IGST on the result
For a sale within one state the GST splits equally into CGST and SGST. For a sale to another state it is charged as IGST. The total is the same either way. Use this reverse calculation when a customer pays a fixed MRP or a quotation is given as an all-inclusive figure and you need the taxable value for the invoice.
Frequently asked questions
- How do I calculate the price before GST from the total?
- Divide the GST-inclusive price by 1 plus the GST rate. For 18% GST, divide by 1.18. The GST amount is the inclusive price minus that result.
- What is the reverse GST formula?
- Price before GST = inclusive price × 100 ÷ (100 + GST rate). GST amount = inclusive price − price before GST.
- Is the result split into CGST and SGST?
- Yes. For an intra-state sale the GST is shown as equal CGST and SGST halves, and for an inter-state sale as IGST. Switch the option to see either.
- Is the amount I enter stored anywhere?
- No. The calculation runs entirely in your browser and nothing is uploaded.