House + Granny Flat Analyser (Australia) - Cash Flow, Yield & Tax by Owner

NEW (24 Oct 2026): Google Sheets edition included. Your download now has the Excel workbook plus a PDF with a one-click link to make your own Google Sheets copy (same formulas, checked cell by cell against the Excel version).

Built and checked by a CPA. Every formula tested against a separate calculation. 30-day money-back guarantee.

NEW in version 1.3 (28 Oct 2026): a clear warning that negative gearing is now limited for established homes bought from 7:30pm AEST 12 May 2026 (a granny flat on an established block is not a new build), so the tax saving shown from 2027-28 may not apply to you.

NEW in version 1.2 (22 Oct 2026): every tab now looks and works like an app screen, not a worksheet: no gridlines or row numbers, a branded header with a one-line instruction on each tab, Home and Dashboard links, cleaner tables and clearly marked input cells. Same tested formulas: every result was checked identical to the previous version.

NEW in version 1.1: a one-page Dashboard with the after-tax cost per week, yields, the granny flat's return and payback, plus 10-year equity and cash-flow charts; a clickable Home page that takes you to every tab; and a cleaner layout throughout. Same tested formulas.

Thinking of building a granny flat, or already own a house with one out the back? See what both dwellings really earn: cash flow, yield, the return on the granny flat build, and the after-tax result for each owner, even when you own it 70/30 or 50/50.

Most property calculators handle one house and one owner. This one is built for a house and a granny flat on one title, often owned in unequal shares. Enter your figures once and get:

• Rent and costs for both dwellings, with vacancy and management fees
• Cash flow before and after tax, per year and per week
• Gross and net yield on the total cost
• The granny flat on its own: return on build cost, cash flow after interest and simple payback years
• Each owner's share of the rental result and change in tax, using 2026-27 resident tax rates
• A 10-year projection: rent and cost growth, loan balance (interest only or principal and interest), property value and equity
• Depreciation inputs for capital works (Div 43) and plant and equipment (Div 40)

What you get: an interactive web version (.html) that opens in any browser and updates as you type, plus the full Excel workbook (.xlsx, 5 tabs). Example figures included.

Who it's for: homeowners deciding whether to build a granny flat for rent, investors buying a house with a granny flat, and couples or family members who own property in unequal shares.

Good to know: owners' tax is simplified (resident rates plus a flat 2% Medicare levy; offsets, HELP repayments and the Medicare levy surcharge are not modelled). Capital gains tax on sale is not calculated.

General information and an estimating tool only, not tax, financial, lending or investment advice. It does not consider your personal circumstances; check results with a registered tax agent or licensed adviser before acting. 30-day money-back guarantee: if it doesn't work for your situation, email hello.plainnumbersco@gmail.com within 30 days. We'll fix it, or refund you in full if you'd rather. This is in addition to your rights under the Australian Consumer Law, which are not excluded. Licence: for the purchaser's own use; please do not resell or share the files.Save more: buying two or more of our tools? Use code BUY2SAVE15 for 15% off orders of A$36 or more, or get all five in the Complete Australian Money Toolkit. Need something we don't sell? We build custom spreadsheets

Designed by Plain Numbers Co with the help of AI tools. Listing images are designed previews of the actual file.