Self-Build Budget Calculator

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.

Frequently asked questions