Can I back-calculate GST if part of the invoice is GST-free

Yes — you can back-calculate GST on a mixed invoice in Law App, where part of the invoice attracts GST and part is GST-free. The trick is to enter the two parts as separate lines: Law App works out the GST on the GST-inclusive line, and the GST-free line is set to 0% GST.

Keeping the lines separate means the GST on the transaction is correct, your clients are charged the right amount of GST, and your BAS (Business Activity Statement) reports the right figures.

How to back-calculate GST on a mixed invoice

Enter the supplier invoice or payment as normal, then split it into one GST line and one GST-free line.

1. Open the supplier invoice or payment and, in the Lines section, click Add.
2. On the first line, enter the GST-inclusive part of the invoice in Gross Amount, with a Tax Category that includes GST. Law App back-calculates the GST for you.
3. Click Add again for a second line.
4. Enter the GST-free part of the invoice in Gross Amount, and set the Tax Category to GST-free (GST = 0%).
5. Check the lines add up to the invoice total, then save the transaction.

Why not back-calculate GST on the whole invoice?

Back-calculating GST on the full invoice total treats the GST-free part as if it included GST. That overstates the GST on the transaction, which flows through to your client’s bill and your BAS.

This covers entering mixed GST and GST-free amounts on supplier invoices and payments in your general (office) account. For help with GST or BAS reporting, contact accounts@lawsupport.com.au (CC support@lawsupport.com.au) or call 07 3040 3036.