How this calculator works
A repair invoice is two businesses in one. Parts are a buying business: what you earn is the gap between what the part cost you and what you charged. Labour is a scheduling business: what you earn depends on how many of the hours you pay for are hours you can bill.
Mixing them into a single "profit" figure hides which half is working. This calculator keeps them apart.
What to enter
- Parts cost — what you paid your supplier, excluding GST.
- Parts charged — what appears on the customer's invoice, excluding GST.
- Labour — hours billed multiplied by your rate, excluding GST.
- Consumables — oil, cleaner, shop supplies. Small per job, material across a month.
- Discount — applied before GST, because that is how it must appear on a tax invoice.
Every figure is pre-tax. GST is collected on the government's behalf and passed on, so counting it as income overstates what the job earned.
Why parts and labour carry different GST rates
Parts are goods and carry an HSN code. Motor vehicle repair labour is a service under SAC 998714, taxed at 18%. The two therefore need separate lines on the invoice, and a single merged line cannot show the correct rate for both. The HSN code finder settles the code for a specific part, and the GST calculator handles the inclusive and exclusive arithmetic.
Getting the job card right first
The numbers here are only as good as the record they come from. If parts issues are written up after the fact, or an approval was never captured, the margin you calculate is a guess. Our guide to the workshop job card format in Excel and Word sets out the columns a card needs, including the GST fields and the approval trail that settles a disputed bill.