Reverse GST Calculation: Find the Base Price from an MRP

You know the final price. You need the pre-GST base amount - for an invoice, an expense entry, or a quotation. Dividing by the GST rate directly is the most common mistake in small-business bookkeeping. Here is the correct method.

The formula

Base amount = Inclusive price × 100 / (100 + GST rate). The GST component is then simply Inclusive price − Base amount. The common error - Inclusive price × GST% - computes tax on the wrong figure and overstates the GST component.

Reverse GST on a ₹1,180 inclusive price across slabs

Where reverse calculation shows up in real business

• Recording expenses from GST-inclusive receipts (fuel, restaurant, retail purchases).
• Quoting a customer a round inclusive price and back-computing the taxable value for the invoice.
• Checking whether a vendor has charged GST correctly on an inclusive quote.
• Splitting the GST component into CGST + SGST (intra-state) or IGST (inter-state) for returns.

CGST/SGST split after the reverse calculation

Once you have the GST component, intra-state supplies split it 50:50 into CGST and SGST; inter-state supplies book the whole component as IGST. Our CGST-SGST-IGST splitter tool automates this second step if you handle both kinds of supplies.