When you only know the final, tax-inclusive price — for example, the amount on a receipt — you often need to know how much of that was the original price and how much was GST. This reverse GST calculator does that backward calculation in one step.
How to Use This Calculator
- Enter the GST-inclusive total amount.
- Select the applicable GST rate.
- Click Calculate to see the original (pre-tax) amount and the GST portion.
How the Calculation Works
Original Amount = Total ÷ (1 + GST Rate / 100)GST Amount = Total − Original Amount
Worked Example
A GST-inclusive total of ₹11,800 at 18% GST: Original Amount = 11,800 ÷ 1.18 = ₹10,000. GST Amount = ₹1,800.
Who Should Use This
Useful for accountants reconciling invoices, buyers checking a vendor's pricing, and sellers who need to report the taxable value from a round, tax-inclusive selling price.
Important Considerations
This calculation assumes the entire amount is taxed at a single GST rate. It does not account for mixed-rate invoices or additional charges like shipping that may attract a different rate.
Common Mistakes
A frequent mistake is simply subtracting the GST percentage from the total (e.g. 18% of ₹11,800) instead of dividing by (1 + rate). That approach overstates the GST amount.
References
Official rates: CBIC GST Portal.