The safe approach is a reconciliation check, not blind trust. GST in Australia is 10 percent, so the GST on a tax invoice should equal one-eleventh of the GST-inclusive total — but per-line rounding on multi-line invoices means the stated GST and the calculated GST sometimes differ by a cent or two. Build the workflow to compute one-eleventh of the total, compare it to the stated GST, and if they differ beyond a small tolerance (say two cents), flag the invoice for human review instead of posting it. That single check is what keeps automated bookkeeping from quietly mis-coding your BAS.
The reconciliation check
In the n8n workflow, after extraction: compute round(total / 11, 2), compare to the stated GST, and branch. If within tolerance, proceed; if not, tag the invoice and send it to a human review queue with both figures shown. Log the decision either way so the trail survives a BAS review. The broader build is in the invoice automation in Australia guide.
Related questions
Should I round GST per line or on the invoice total?
Follow the supplier invoice and your accounting system. The ATO accepts either the total-invoice rule or the taxable-supply rule, but your posted bill should match what is on the tax invoice. The workflow should preserve the supplier stated figures and only flag genuine mismatches, not re-derive GST and overwrite it.
Can the workflow assign the right GST tax code automatically?
Yes — map each line to the correct Xero/MYOB tax code (GST on Expenses, GST Free, Input Taxed) using supplier and line rules, and route anything ambiguous to review. Most GST errors come from wrong tax codes, not arithmetic.
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