The Free Granny Flat Cost Calculator
Most builders quote the kit price or lock-up price and rarely reveal the real number until you’ve signed. Use this free on-page tool to budget for what they leave out: council fees, sewer, electricity and site works.
Four Phases of Your Real Budget
A finished granny flat is far more than the build price. Here is where the money actually goes.
Preliminaries
Illustrative allowances for design, reports and approvals. Obtain the actual fees for your address.
Site Costs
Earthworks, water connection, sewer trenching, electrical metering and stormwater. The big variable on most blocks.
The Build
Slab, frame, cladding and roofing. The part most quotes focus on.
Finishes
Turn-key items: flooring, painting and the kitchen that make it liveable.
- Preliminaries. Surveys, soil tests, certifier fees and state-based council allowances.
- Site costs. Earthworks, water, sewer, electricity meter and crane access.
- Build + finishes. Slab to lock-up, then kitchen, bathroom and fit-out.
- Build-type aware. Traditional, modular and kit DIY each priced differently.
How To Use This Estimator
Test an illustrative budget scenario. These presets are not market averages; replace assumptions with written project quotes.
Choose your build type
Pick traditional on-site, modular transportable, or a kit DIY build. Each carries a different cost profile.
Input your square meterage
The tool applies roughly $2,300 to $3,800 per sqm turnkey, depending on finish level and build type.
Add the hidden variables
Pick your state, approval path, slope, sewer run and electrical connection. These move the total more than finish level alone.
Granny Flat Cost Calculator
Updated for June 2026 Australian cost bands. All calculations run in your browser: nothing is saved or sent anywhere.
Project details
Pick a layout preset or adjust each field to match your block and build plans.
Rental yield & finance (optional)
Line-item estimate
Every allowance in your total, updated as you change inputs above.
| Item | Allowance |
|---|---|
| Certifier / CDC fees | $5,500 |
| State council contribution allowance | $9,000 |
| Earthworks, slab & access | $15,000 |
| Water connection | $2,500 |
| Electrical connection | $5,500 |
| Lock-up build (slab to roof) | $136,800 |
| Kitchen, bathroom & fit-out | $34,200 |
Quote exclusion comparator
Use this when a supplier quote looks cheaper than the calculator. Lines below are planning allowances, not a bill of quantities. Confirm with your certifier and the written quote.
| Item | In this calculator | Supplier scope to confirm | What to check |
|---|---|---|---|
| Site works | Earthworks, slab and access allowance | Often excluded or capped | Sloping, rock, retaining and driveway extras sit outside most kit prices. |
| Crane | Optional crane hire line | Check the contract | Ask the supplier and lifting contractor whether a crane is needed for this delivery. |
| Foundation | Included in earthworks/slab allowance | Sometimes a separate engineer package | Reactive clay and flood overlays change the footing design. |
| Approvals | Certifier/CDC or DA consultant allowance | Confirm who arranges and pays | Confirm the planning and building route for your jurisdiction. CDC and DA are NSW examples. |
| Utilities | Water, sewer, electrical and stormwater lines | Often excluded beyond a short run | Obtain connection quotes for the address and compare them with the supply scope. |
| Transport | Kit delivery allowance inside site costs | Confirm delivery scope | Regional haulage and escorts are rarely in a metro display price. |
| Finishes | Kitchen, bathroom and fit-out phase | Shell-only kits omit joinery | Appliance packs and tiling grades change this line quickly. |
| Landscaping | Optional fencing and basic landscaping | Check the contract | Privacy screens, turf and retaining are owner costs unless written in. |
Download a summary with the copy button above, then paste it beside any quote. The Granny Flat Guide is an editorial research hub, not a licensed builder or certifier.
Assumptions behind this scenario
The inputs below are illustrative, not a surveyed price dataset. The range is not a confidence interval. Rent calculations exclude land, vacancy, expenses, finance costs and tax.
| Assumption | Model input | How to use it |
|---|---|---|
| Build-rate inputs | $2,300 / $2,850 / $3,800 per m² | Illustrative rates before the model adds other phases; not observed market prices. |
| State allowance | $2,800–$9,000 plus a $5,500 base | Model inputs, not council contribution schedules or certifier quotes. |
| Displayed range | 15% below and above the model total | A sensitivity band, not a statistical confidence interval or accuracy promise. |
| Site and energy options | Fixed amounts shown in the controls | Illustrative additions; obtain the required design and installed quotes. |
| Rent and finance | Your selected weekly rent, deposit, rate and term | Scenarios only; no rental appraisal, lender approval or tax calculation. |
Primary sources
Size caps, approval pathways and dollar bands on this page are planning ranges. Check the current official page before you lodge or sign.
See our editorial standards for how we research and update guides.
Got a number? Here's what to do with it
Use your estimate as a sanity check when you dig deeper into the research or contact suppliers yourself.
Ready to Ask a Follow-Up Question?
Most homeowners use the calculator first, then browse directories or message us if something is unclear. Your enquiry stays with our inbox.
Send an enquiryAlready talking to suppliers? Read our guides to spot what might be missing from a quote.
Cost Calculator FAQs
Quick answers before you start budgeting.
Is the granny flat cost calculator free?
Yes. Use the calculator without signing up or downloading a file.
How accurate is the result?
We have not validated a percentage accuracy against completed projects. The rates, state allowances and range are illustrative assumptions, not market averages or a quote.
Are approval fees confirmed?
No. Obtain the applicable authority charges and practitioner quotes for your property. The approval selector does not determine eligibility.
Does it predict investment returns?
No. Gross rent divided by the modelled build cost excludes land value, vacancy, operating expenses, finance costs and tax. The cost-to-gross-rent ratio is not an investment payback forecast.
Which building method is cheapest?
Compare complete quotes for the same scope. Model assumptions cannot establish which supplier or construction method offers the lowest completed-project price.
Can I share a scenario?
Use the share link to retain the selected inputs in the URL fragment. Check those inputs and replace assumptions with your own project evidence before relying on the result.
Related Guides & Tools
Budgeting is step one. These pages help with the decisions that follow.
