GST Calculator
Add GST to a net price or extract the base price from a GST-inclusive total.
Calculation Examples
How to Use the GST Calculator
Start by entering either the Net Price (before tax) or the Gross Total (tax included). Then select the GST rate. Since 22 September 2025, India has two main slabs, 5% and 18%, plus 40% for select luxury and sin goods. The old 12% and 28% slabs were removed. Enter a custom percentage for special-rate goods or for supplies made before that date.
Then choose the direction. Select Add GST to find the invoice total from a base price, or Remove GST to extract the base value from a tax-inclusive amount. The results show the GST amount, net price, gross total, and the CGST/SGST or IGST split for the transaction type you pick. This helps in B2B invoicing, where small rounding differences in tax lines can cause reconciliation problems during GST portal filing.
The Algebraic Logic Behind GST Calculations
The calculator uses two formulas, depending on the direction of the calculation.
For tax-exclusive pricing, where GST is added on top of the base price: \[\text{Total} = \text{Base} \times \left(1 + \frac{\text{Rate}}{100}\right)\]
For tax-inclusive pricing, where the GST is extracted from a known total: \[\text{GST Amount} = \text{Total} - \frac{\text{Total}}{1 + \frac{\text{Rate}}{100}}\]
For intra-state supplies, the total GST splits equally into CGST and SGST, each half the rate. For inter-state supplies, the full rate applies as a single IGST line. The split decides which tax heads your Input Tax Credit (ITC) lands in, so it must be right in your monthly GSTR filings. Rates here follow the structure approved by the 56th GST Council meeting (3 September 2025).
Useful Tips 💡
- Apply GST to the value after trade discounts shown on the invoice, so you do not tax an amount that was never charged.
- Identify the Place of Supply before choosing between CGST/SGST and IGST.
- For a supply made before 22 September 2025, use the custom rate field with the old rate (12% or 28%), because the rate depends on the time of supply, not the date you file.
📋Steps to Calculate
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Enter the net price or gross total amount.
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Select the GST rate (5%, 18%, 40%) or enter a custom rate.
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Choose Add GST or Remove GST, then select intra-state or inter-state to see the CGST/SGST or IGST split.
Mistakes to Avoid ⚠️
- Calculating GST on a price that already includes GST, which creates a tax-on-tax error and inflates the liability.
- Applying the wrong rate because of an HSN code mismatch, such as using 5% on a good that falls under 18%.
- Using the old 12% or 28% slab for a supply made on or after 22 September 2025.
- Treating exempt or nil-rated supplies as taxable, which leads to unnecessary tax collection.
Practical Applications📊
Verify the GST amount on vendor invoices before you process accounts payable.
Calculate Reverse Charge Mechanism (RCM) liability for notified services.
Work out the tax-inclusive shelf price of a product, for example Rs. 2,000 at 5% GST sells at Rs. 2,100.
Estimate quarterly GST outflows for cash flow planning.