Sales Documents
GST, TDS & TCS calculations
Exactly how Billing computes CGST/SGST, IGST, TDS, TCS, and the invoice total.
Per-line tax
For each line, tax is computed on the taxable value (unit price × quantity):
- tax = round(taxable × rate_bps ÷ 10000) where a rate of 18% is 1800 basis points.
Intra-state vs inter-state
- Intra-state (default): the tax splits into CGST and SGST. CGST is the floor of half the tax; SGST is the remainder, so the two always add back to the exact tax (no rounding loss).
- Inter-state (IGST): tick Inter-state supply. The whole line tax becomes IGST; CGST and SGST are zero.
The GST summary panel shows Taxable value, then either IGST or CGST + SGST.
Document totals
Across all lines:
- Subtotal = sum of taxable values.
- Tax = sum of line taxes.
- TDS = round(subtotal × tds_rate_bps ÷ 10000), subtracted from the total.
- TCS = round(subtotal × tcs_rate_bps ÷ 10000), added to the total.
- Total = max(0, subtotal + tax + TCS − TDS).
TDS shows as a negative line and TCS as a positive line in the summary. If no TDS/TCS rate is selected, both are zero.
Validation
- A line needs a description and a non-negative unit price to save.
- A customer and at least one valid line are required before you can save or issue.
- Selecting TDS/TCS requires those masters to exist; otherwise the fields show None with a link to add rates.
Snapshot on issue
When you issue, the computed totals and tax are snapshotted onto the document, so later master changes do not alter an issued invoice.