Self-Build Budget Calculator
Build a complete self-build budget from plot price, construction cost, professional fees, contingency, services and finance.
💼 Are you a real estate agent or broker? Send this calculator to your buyers on your own branded listing page — every enquiry comes straight to your WhatsApp. Create free agent page →Self-builds run out of money in predictable places: the plot costs more than the price because of buying costs, the build costs more than the quote because of fees and contingency, and the services connections were never in anyone's budget at all.
Setting the full cost against the finished value is what shows whether the project makes sense financially as well as personally. A negative margin is not automatically a reason to stop, but it should be a known number rather than a discovery.
How the budget builds up
Plot price plus buying costs, then construction at a rate per unit area with professional fees and contingency applied in sequence, then services connections and the cost of financing the build. The margin is the finished value less that total.
Worked example
A 150,000 plot with 5% buying costs is 157,500. Building 2,200 square feet at 200 is 440,000, plus 12% fees and 10% contingency brings it to 542,080. Adding 12,000 of services and 21,000 of finance gives 732,580 against a finished value of 850,000 — a margin of 117,420, or about 333 per square foot of total cost.
Test it at a lower value and a higher cost
Self-builds routinely overrun on both. Re-run this with the build rate 15% higher and the finished value 10% lower: if the margin survives that, the project is robust. If it does not, the plot price is probably too high.
Turn a calculation into an enquiry
Buyers who run these numbers are ready to talk. Give every listing its own page with your photo, phone and WhatsApp on it — leads land straight on your phone.
Create your free property pageFrequently asked questions
What is usually missing from a self-build budget?
Services connections, the cost of finance during the build, temporary accommodation while building, and the landscaping and driveway at the end. Together these routinely add ten percent that nobody planned for.
How much contingency is enough?
Ten percent is a minimum on a new build with good ground conditions, and more where the site is sloping, has poor access, or the ground has not been investigated. Groundworks are where the surprises live.
Is self-building cheaper than buying?
It can be, largely because you capture the developer margin, and it is far more work and risk. The margin here is payment for both, not free money, and it can vanish entirely on an overrun.