If you sell goods or services and quote GST-inclusive prices to customers but need GST-exclusive figures for your books (or vice versa), getting the conversion direction wrong is a surprisingly common — and costly — mistake.
The two prices, defined
A GST-exclusive price is the base amount before tax is added. A GST-inclusive price already has GST built in — it's the final amount the customer pays. The same underlying sale has two different numbers depending on which convention you're using, and they should never be used interchangeably without converting first.
Where sellers go wrong
The most common error is applying the GST rate directly to an inclusive price as if it were exclusive — for example, taking an inclusive price of ₹11,800 at 18% GST and calculating "GST" as 18% of ₹11,800 (₹2,124) instead of the correct ₹1,800. This happens because the correct formula for extracting tax from an inclusive price divides by (1 + rate/100) rather than simply multiplying the rate.
The correct formulas
Going from exclusive to inclusive: Inclusive = Exclusive × (1 + Rate/100). Going from inclusive to exclusive: Exclusive = Inclusive ÷ (1 + Rate/100). Our GST Inclusive Exclusive Calculator handles both directions and shows them side by side, so you can sanity-check an invoice in seconds.
When you only have the final price
If you only know the tax-inclusive total — say, from a receipt — and need to know how much of it was tax, that's a reverse calculation. Our Reverse GST Calculator is built specifically for that case, extracting both the base amount and the GST portion from a single inclusive total.
Don't forget the CGST/SGST split
Once you know the correct GST amount, remember that for a sale within the same state, it splits equally into CGST and SGST — not the full amount under one head. Our CGST SGST Calculator shows this split, and also the IGST equivalent for inter-state sales, which is useful when deciding which tax fields to fill in on an invoice.
Practical takeaway
Before finalising any price list or invoice template, run a couple of your real numbers through a GST calculator and confirm the inclusive and exclusive figures match what you expect — it takes under a minute and prevents under- or over-charging customers, or misreporting your taxable value.