NSW variation price calculator

Pricing variations on NSW residential jobs

Markup or margin?

Markup is added on top of cost: $2,500 cost with 20% markup is $3,000 excl. GST. Margin is the share of the selling price that is profit: to make a 20% margin on $2,500 cost you need $3,125 excl. GST, which is a 25% markup. Mixing the two up means the variation is priced lower than you intended. The calculator shows both figures so you can check.

Put it in writing and get it signed

For contracts covered by the Home Building Act 1989 (NSW), Schedule 2 says any agreement to vary the contract, or its plans and specifications, must be in writing and signed by or on behalf of each party. NSW Government guidance also says the variation document should explain the cost and its effect on the overall contract price, and show how the price change was calculated rather than just a dollar amount. Before starting the work, give the owner a written description, any plans or specifications, the extra cost and any extra time.

The NSW Court of Appeal has held that an oral variation can’t be enforced under the contract (Xu v Jinhong Design & Constructions [2011] NSWCA 277). Getting the signature first protects your payment.

Credits for deleted work

If the owner deletes work, enter it as a negative cost. Whether you can keep a margin on deleted work depends on your contract, so check its variation clause.

Extra time

Write any extra time on the same variation so the completion date moves with it. Use the NSW working days calculator to turn working days into a new date.

General information only, not legal or financial advice. Check your own contract’s variation clause and get advice for your situation. Sources: Home Building Act 1989 (NSW) Sch 2 cl 1(2); NSW Government, Contracts for residential building work; checked October 2026.