The conversation usually starts the same way. The kids' rooms are too small, or too empty. The kitchen worked for four and doesn't work for eight at Christmas. Someone says, half-seriously, "maybe we should just move."
Then someone opens a real estate app, sees what the next house up costs, and the room goes quiet.
That's the point where most families start comparing numbers — and where most of them compare the wrong ones.
The moving costs people forget
The purchase price is the number everyone looks at. It's not the number that decides this.
Moving in Victoria carries a stack of costs that never show up in the listing: stamp duty on the purchase, agent commission and marketing on the sale, conveyancing on both ends, building and pest inspections, removalists, and the gap between settlements. Stamp duty alone is usually the largest single cost in the exercise and it buys you nothing you can live in.
And there's a structural problem underneath it. You are selling into the same market you're buying into. If your suburb has risen, so has the one you're moving to. You are not stepping up as far as the difference between the two prices suggests.
The extension costs people forget
Extending has its own hidden list, and pretending otherwise doesn't help anyone.
Design and documentation. Planning and building permits, and any reports the council or overlays require. Construction, which is the big one. A contingency that is genuinely held, not notionally held. Somewhere to live if you can't stay in the house. Holding costs while it runs — and this is a long process, not a fast one.
There's also a ceiling. Every suburb has a price above which further spending is unlikely to come back on resale. Spending past it isn't automatically wrong — plenty of people build a forever home deliberately — but it should be a decision made on purpose, not discovered afterwards.
The question that actually decides it
Here's the honest version: this is rarely a cost comparison. Run properly, the two numbers usually land closer together than people expect.
What separates them is what the money buys.
Moving buys a different house, a different street, and a different set of compromises — because the new house will have its own. Extending buys a house shaped around how your household actually lives, in the suburb you already chose, with the school, the neighbours and the commute intact.
The real question is narrower and more useful: can this block deliver the home you want?
Sometimes it can't. Orientation, slope, an easement, a planning overlay, the setbacks, the neighbour's boundary — occasionally the honest answer is that this site will not give you what you're asking of it, and the money is better spent moving. It's better to find that out for the cost of a feasibility study than after a design is drawn.
What to do next
Start with the block, not the budget. A feasibility study tests what your site and the planning controls will genuinely allow, sets out the options, and puts a cost estimate against them — so the extend-or-move decision gets made with real numbers instead of a real estate app and a guess.