If I could teach you one thing about land subdivision, it would be this: never proceed on a deal unless it shows a minimum 30% margin on total costs.
Not 15%. Not 20%. Not "close enough." Thirty percent. That's the number that has protected me across more than 30 projects and $300 million in development value. It's the number I teach every student in the LandED program. And it's the number that will protect you when things don't go exactly to plan. Because they never do.
This guide explains what the 30% margin rule actually means, why the number is set where it is, how to calculate it yourself on any site in Australia, and what to do when a deal falls short.
What is the 30% margin rule?
The 30% margin rule is simple. Before committing to a subdivision project, you calculate your expected profit as a percentage of your total costs. If that percentage isn't at least 30%, you don't proceed.
The "total costs" include everything: the purchase price of the site, all subdivision costs (council fees, civil works, professional fees), holding costs (rates, insurance, interest), and selling costs (agent commissions, marketing). The profit is what's left after all of those are subtracted from your Gross Realisation Value, which is what you expect to sell the finished lots for.
Here's a simple way to think about it. If your total costs are $500,000, you need to sell the finished lots for at least $650,000 to hit a 30% margin. That $150,000 difference is your gross profit, and $150,000 divided by $500,000 equals 30%.
"The 30% margin rule isn't about being greedy. It's about being protected. Every project I've ever done has had at least one thing that didn't go to plan. The margin is what absorbs those surprises and still leaves you with a profit."
Why 30%? Why not 20% or 40%?
This is a question I get asked all the time. The answer comes from experience, not theory.
At 20% margin, you have almost no room for error. If your civil works come in $15,000 over budget, or your project takes three months longer than expected (adding holding costs), or the market softens slightly and you sell for 5% less than you forecast, your profit evaporates. A deal that looked like a $100,000 win on paper becomes a $20,000 win or even a loss in reality.
At 30%, you have a genuine buffer. Those same surprises, which happen on almost every project, reduce your margin but don't eliminate it. A 30% deal that encounters $30,000 in unexpected costs and a 5% reduction in sale price might end up delivering 18% to 22%. That's still a very good result.
At 40% or above, you're in excellent territory, but those deals are rarer. If you hold out for 40% margins on every deal, you'll reject too many viable opportunities. Some of my best projects came in at 28% to 35% on paper and delivered 22% to 30% in reality. That's the sweet spot.
Some property educators talk about margin as a percentage of the sale price (revenue). We calculate it on costs, not revenue. The reason is practical: margin on costs gives you a more conservative and more useful number. A 30% margin on costs is roughly equivalent to a 23% margin on revenue. If someone tells you a deal has a "25% margin" and they're calculating it on revenue, the margin on costs is actually closer to 20%, which isn't enough buffer.
The formula explained
The calculation has four components. Once you understand each one, you can run a feasibility on any site in under 20 minutes.
1. Gross Realisation Value (GRV)
This is what you expect to sell the finished lots for, combined. If you're doing a 1-into-2 subdivision and each lot is worth $450,000, your GRV is $900,000. If you're doing a 1-into-3 and the lots are worth $380,000, $380,000, and $350,000 (corner lots are sometimes worth less), your GRV is $1,110,000.
Getting the GRV right is the most important part of the entire feasibility. If you overestimate what the lots will sell for, your margin is fiction. I'll cover how to estimate GRV accurately later in this guide.
2. Total acquisition cost
This is the purchase price of the site plus all costs associated with buying it: stamp duty, legal fees, building and pest inspections, and any other due diligence costs. Stamp duty varies significantly by state and price point. As a rough guide, budget 3% to 5.5% of the purchase price for stamp duty plus legal costs combined.
3. Total project costs
This covers everything you spend to turn one lot into multiple lots:
- Town planner fees: Preparing and lodging the development application
- Surveyor fees: Boundary survey, plan of subdivision, certification
- Civil engineering: Design of roads, drainage, stormwater, retaining walls
- Civil construction: The actual earthworks, road construction, drainage installation
- Council fees: DA application fees, infrastructure charges, headworks
- Service connections: Water, sewer, stormwater, power, telecommunications for each new lot
- Holding costs: Rates, insurance, loan interest for the duration of the project
- Contingency: A buffer for unexpected costs (I use 10% of project costs)
4. Selling costs
Agent commissions (typically 2% to 2.5% of sale price plus GST), marketing costs, and legal fees for settlement. Some people sell their lots privately to save on commissions, but budget for agents regardless because it gives you a more conservative feasibility.
The formula
Gross Profit = GRV minus Total Acquisition Cost minus Total Project Costs minus Selling Costs
Margin on Costs = Gross Profit divided by (Total Acquisition Cost + Total Project Costs + Selling Costs) x 100
If that number is 30% or above, the deal is worth pursuing. If it's below 30%, walk away.
Worked example: A real 1-into-2 subdivision
Let's walk through a real-world example. This is based on a typical 1-into-2 infill subdivision in a southeast Queensland suburb, the kind of deal that's bread and butter for first-time subdividers.
The site
A 920 square metre block in a Low Density Residential zone with a minimum lot size of 400 square metres. Flat site, all services in the street, no overlays. The plan is to subdivide into two lots of approximately 460 square metres each.
This deal passes the 30% rule. Even if civil works come in $10,000 over, or the lots sell for $10,000 less each, the margin still holds above 25%. That's a deal worth pursuing.
Want to run these numbers on your own site?
The Master Land Subdivision online course includes a downloadable feasibility calculator that runs this exact calculation for any Australian site, plus Adam's cost assumptions by state.
Get the Online Course →Knowing your cost inputs
The most common mistake in feasibility calculations is underestimating costs. People forget items, use optimistic numbers, or skip the contingency. Here's how to avoid that.
Always include a contingency
I use a 10% contingency on project costs (not including the purchase price). On a project with $150,000 in subdivision costs, that's $15,000 set aside for surprises. In my experience, you'll use some or all of it on almost every project. Unexpected soil conditions, an extra council requirement, a service connection that's more complex than quoted. The contingency is not optional.
Use realistic holding cost assumptions
Your project will take longer than you think. Council assessment periods vary, but 6 to 12 months for a DA decision is common in most Australian states. Add civil works (2 to 4 months) and settlement (1 to 3 months), and you're looking at 12 to 18 months from purchase to receiving your money. Budget your holding costs accordingly: loan interest, rates, insurance, and land tax for the full period.
Budget for selling costs even if you plan to sell privately
If you end up needing an agent, you don't want that to be the thing that pushes your margin below viability. Budget 2.5% of sale price plus GST for agent commissions, plus $2,000 to $5,000 for marketing per lot. If you sell privately and save those costs, it's upside.
Typical subdivision costs by state
These are indicative ranges for a standard 1-into-2 residential subdivision. Actual costs vary significantly by council, site conditions, and project complexity. Use these as starting points for your back-of-envelope feasibility, not as quotes.
Infrastructure charges are the most variable cost. Some councils charge $10,000 per additional lot. Others charge $40,000 or more. In Queensland, infrastructure charges are often the single biggest line item after the land purchase itself. Always confirm these with the specific council before finalising your feasibility.
How to estimate your GRV
Your Gross Realisation Value is the number that makes or breaks the feasibility. Get it wrong, and everything else is irrelevant.
Use recent comparable sales
Look at sales of vacant lots of similar size in the same suburb within the last 6 to 12 months. Use realestate.com.au's "sold" filter or Domain's recent sales to find these. You want at least three comparable sales to establish a reliable range.
Match the lot characteristics
A 450 square metre lot on a quiet street is not comparable to a 450 square metre lot on a main road. Match the characteristics as closely as possible: lot size, street type, position (corner vs mid-block), slope, views, and proximity to amenities. If your subdivided lots will be slightly inferior to the comparables (smaller, less frontage, battleaxe access), adjust downward.
Be conservative
Use the lower end of the comparable range, not the top. If similar lots have sold for between $480,000 and $530,000, use $490,000 in your feasibility. The market might be at $530,000 when you complete, or it might have softened to $470,000. Using a conservative GRV means your 30% margin is more likely to survive reality.
"I've never regretted being conservative on GRV. I've seen plenty of people regret being optimistic. The market doesn't care about your spreadsheet."
The 5 things that kill margin
After 30+ projects, I can tell you that most margin erosion comes from the same five sources. If you can control or anticipate these, you'll protect your returns on almost every deal.
1. Overpaying for the site
The purchase price is the single biggest cost in any subdivision. If you pay too much, no amount of cost management will save the margin. This is why the back-of-envelope feasibility should be the very first thing you do, before you get emotionally attached to a site.
2. Underestimating infrastructure charges
Infrastructure charges (also called headworks or developer contributions) are set by the council and are often non-negotiable. They can range from $10,000 to $50,000+ per additional lot depending on the council. Always confirm the exact charges before you finalise your feasibility. A phone call to the council's development assessment team usually gets you the answer.
3. Unexpected civil works
Rock under the surface. A stormwater pipe that needs relocating. A retaining wall you didn't anticipate because the contour survey showed a gentle slope but the reality was steeper. Civil works are the most common source of cost blowouts. A good civil engineer and a proper site inspection reduce this risk significantly.
4. Timeline blowouts
Every extra month your project takes is another month of holding costs. Interest on your development finance, rates, insurance, land tax. On a project with $600,000 in debt, holding costs can run $3,000 to $5,000 per month. A 6-month delay costs you $18,000 to $30,000. Build realistic timelines into your feasibility, and add a buffer.
5. Overestimating end values
If you assume your lots will sell for $520,000 and they actually sell for $480,000, that's $80,000 less revenue on a 1-into-2 deal. On a project with a 30% margin, that could halve your profit. Always use conservative GRV estimates based on recent comparable sales, not agent appraisals or wishful thinking.
What if a deal shows below 30%?
Walk away. That's the short answer.
The slightly longer answer is that there are only three ways to improve a deal's margin:
- Pay less for the site. If the vendor will accept a lower price, the margin improves. But don't assume they will. Use the feasibility to work out the maximum price you can pay while still hitting 30%, and offer that.
- Reduce costs. Sometimes you can reduce costs by choosing a simpler subdivision layout, avoiding expensive civil works, or negotiating better consultant fees. But be careful not to cut the contingency, because that's what protects you.
- Increase GRV. This is the hardest lever to pull. You can't make the market pay more than it wants to. Sometimes holding for 6 to 12 months in a rising market will lift values, but that's speculation, not a strategy.
If none of those three options gets you to 30%, the site isn't the right deal. Move on. There are always more sites. The discipline of walking away from deals that don't hit the number is what separates people who consistently build wealth from people who occasionally get lucky.
A deal one student walked away from, and the better deal he found 3 weeks later
One of our students found a site in suburban Brisbane that looked perfect on paper. Great street, right zone, no overlays. But when he ran the feasibility, it came in at 24% margin. The purchase price was firm because the vendor knew the subdivision potential.
He walked away. Three weeks later, he found a comparable site two suburbs over where the vendor was an elderly couple who had no idea about the subdivision potential. He secured it at a price that gave him a 36% margin. Same amount of work. Same timeline. But $60,000 more profit, because he had the discipline to wait for the right numbers.
What comes next
The 30% margin rule is the foundation of every decision in a subdivision project. But running a feasibility is only useful if you know how to find sites worth running the numbers on, and if you know what to do after the numbers confirm a deal is viable.
If you haven't already, read our guide on How to Find Subdivision Sites Using Free Online Tools. That guide shows you the exact process for building a pipeline of sites to run feasibility on.
For a detailed breakdown of what each cost item looks like in practice, our upcoming guide on Land Subdivision Costs in Australia covers the specific numbers state by state.
If you want to understand whether you're ready to start looking at deals, take our free readiness quiz. It gives you a clear picture of where you stand and what your next step should be.
And if you're ready to work through real feasibility calculations on real sites with a step-by-step framework and downloadable tools, the Master Land Subdivision online course covers everything in this guide and more, in detail.
The numbers don't lie. Learn to trust them, and they'll tell you exactly which deals to pursue and which to leave alone.
