GST Calculator Guide for Contractors — Everything Aussie Tradies Need to Know

GST confuses most tradies. Do you register? When? How do you add it to quotes? What can you claim back? Here's the complete guide — plus a free GST calculator built into every quote template.

When Do You Need to Register for GST?

You must register if your annual turnover is $75,000+. You can register voluntarily under $75k — and sometimes that's smart.

• Must register: $75,000+ in annual turnover
• Voluntary registration: You can register below $75k
• Exceptions: Ride-sourcing (Uber drivers) must register regardless

How to Add GST to Your Quotes

Simple: multiply your pre-GST price by 1.1.

Pre-GST price: $5,000\nGST (10%): +$500\nTotal quote: $5,500

Important: Always show GST as a separate line item on quotes and invoices. It's legally required and builds trust with clients.

What GST Can You Claim Back?

Almost everything you buy for your business includes GST. As a registered business, you claim it back on your BAS.

• Materials & supplies (timber, concrete, pavers, paint)
• Tools & equipment
• Vehicle expenses (fuel, servicing, tyres)
• Phone & internet (work %)
• Insurance premiums
• Marketing & advertising
• Accountant & bookkeeper fees
• Software subscriptions (Xero, Tradify, AroFlo)

BAS Lodgement: Quarterly vs Annual

Most tradies lodge quarterly. Key dates:

• July–Sept Qtr: Due 28 October
• Oct–Dec Qtr: Due 28 February
• Jan–Mar Qtr: Due 28 April
• Apr–Jun Qtr: Due 28 July

Common GST Mistakes Tradies Make

1. Forgetting to put aside 1/11th of every invoice for the ATO
2. Claiming GST on non-business purchases (that Bunnings BBQ? No.)
3. Not keeping receipts — the ATO is going paperless and expects digital records
4. Double-claiming: fuel AND km method — pick one
5. Missing BAS deadlines — automatic penalties apply