How do I know if a supply is intra-state or inter-state?
By place of supply against your registration — not by where the goods physically went. Same state means CGST plus SGST; different states means IGST.
Can an invoice carry both CGST and IGST?
No. A single supply is one or the other. An invoice showing both is an error, and it is a common one when tax is decided at the total rather than at the line.
What is 'tax included' for?
When you have a gross figure and need to work backwards — common with retail pricing. The calculator extracts the taxable value from the total.
Are these all the rates?
These are the common slabs. Special rates exist for particular goods, and cess applies on top for some categories — which this calculator deliberately does not guess at.
Does rounding matter?
Yes. Autobooks rounds each result to two decimals and auto-corrects a total difference of ₹1 or less through the Round-Off ledger; anything larger is refused rather than absorbed.