About this tool
A reverse GST calculator works backwards from a price that already includes tax. If a shop bill says 11,800 and the goods are taxed at 18%, the taxable value is not 11,800 minus 18%. It is 10,000, and the GST is 1,800. This tool does that conversion for you and also works forward when you have a pre-tax price and want the final amount.
Choose whether your amount includes GST or excludes it, pick a standard slab or type your own rate, and tick the intra-state option when you want to see the tax split equally into CGST and SGST.
How to use the Reverse GST Calculator
- Type the bill or price into the Amount field.
- Select "Yes" if that amount already contains GST, or "No" if GST still has to be added.
- Choose 5%, 12%, 18% or 28%, or pick Custom rate and type your own percentage.
- Leave the intra-state box ticked to see CGST and SGST, or untick it for an inter-state sale where the full amount is IGST.
- Press Calculate, then use Copy result to paste the figures into your invoice or notes.
Practical examples
How it works
For a GST-inclusive amount, the tool uses: taxable value = inclusive amount x 100 / (100 + rate). GST = inclusive amount - taxable value. Dividing by (100 + rate) is what separates this from the common mistake of subtracting the percentage from the total.
For a GST-exclusive amount: GST = amount x rate / 100, and the final amount = amount + GST. For intra-state supplies the GST is shared equally, so each of CGST and SGST is half the rate. Results are shown rounded to two decimals; your invoice rules may round differently.
Privacy and file processing
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Frequently asked questions
Why is 18% of 11,800 not the GST amount?
Because 11,800 already contains the tax. The GST is 18% of the pre-tax price (10,000), which is 1,800, or 18/118 of the total.
When do I use CGST and SGST instead of IGST?
CGST and SGST apply when the seller and the place of supply are in the same state. For supplies across states, IGST at the full rate applies instead.
Can I use a rate that is not 5, 12, 18 or 28?
Yes. Choose Custom rate and enter any value between 0 and 100, such as 3% or 0.25%.
Is this a substitute for an accountant?
No. It is an arithmetic aid. Rates and rules change, so confirm the applicable rate for your goods or services with the official GST rate schedule or a professional.
Related tools
Results are for general information. Check important figures against official sources. Read the disclaimer.