House Construction Cost Calculator

About the House Construction Cost Calculator

Plan the budget for building a house. Enter the built-up area of each floor and the rate your contractor quotes per sq ft or m² (a floor can have its own rate), or list the work item by item with your own quantities and rates. The calculator adds a contingency allowance, GST at the rate on your contractor’s invoice and professional fees, and shows the total, the cost per sq ft and what each floor costs.

The cost is then split into stages — foundation, frame, walls, plaster, flooring, doors and windows, electrical, plumbing and finishing — and turned into a stage-wise payment plan with a running total, ready to copy, download or print. Every rate and share is yours to set: the calculator never assumes a market rate.

Common uses

• Budgeting a new house, a floor added on top or an extension before taking quotes.
• Comparing contractors’ quotes per sq ft on the same area.
• Planning stage-wise payments and loan disbursements.
• Sharing a simple estimate with family, a lender or the contractor.

How the estimate is built

• Construction cost = Σ (floor built-up area × rate), or Σ (item quantity × item rate).
• Contingency = construction cost × contingency % — an allowance for price rises, surprises on site and changes you make.
• GST = (construction + contingency) × the GST % on the contract.
• Professional fees = (construction + contingency) × fees %, plus GST on the fees if your consultant charges it.
• Total = construction + contingency + GST + fees + GST on fees; cost per sq ft = total ÷ total built-up area.
• Each floor gets its share of the contingency, GST and fees in proportion to its construction cost, so the floors add up to the total.
• Each stage of the payment plan gets its share of the contingency and GST, so the stages add up to what the contractor is paid. Professional fees go to your consultants and are shown outside the plan.

Choosing the rate

A rate per sq ft is only comparable when you know what it covers: material and labour or labour only, the grade of finishes (tiles, fittings, paint, doors and windows), the structure (number of floors, foundation type) and whether electrical and plumbing work, the staircase, water tanks and the compound wall are included. Ask each contractor for the same specification, or itemise the work from a bill of quantities and enter the items with their own rates.

Stages and the payment plan

Building contracts often pay the contractor as work is completed, stage by stage. The calculator starts with nine stages and an example split so that the plan has something to show — the shares are placeholders, not a standard, and real projects differ a lot. Replace them with the stage percentages in your contract or your engineer’s estimate. The payment plan shows each stage’s share of the work (with its contingency and GST) and the running total, so you can line up your savings or loan disbursements with the work.

GST and fees

GST depends on how the work is contracted — for example a composite contract for material and labour, labour only, or materials you buy yourself — so the calculator applies the rate you enter. Use the rate shown on your contractor’s and your architect’s GST invoices, or 0 % if they are not registered or the rate already includes it.

Limitations

• An estimate from your own rates, not a professional cost estimate or a bill of quantities. Have an engineer or quantity surveyor price the actual design before you sign a contract.
• Land, approvals and permit fees, utility connections, interiors, furniture and landscaping are not included unless you add them as items or floors.
• The stage split is an example to edit; it is not a standard for any type of building.

Privacy

Everything happens in your browser. What you enter or open here is not uploaded or stored by MySmartCoPilot.