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Day 04 · The Prompt SeriesLIVE

Investor Cash FlowStress Test.

Modelling gross yield is easy. Modelling what an investment property actually costs after vacancy, management fees, rates, insurance, and a 2% rate rise is the analysis most investors never run. Three minutes. Base case, bear case, and survival case.

Why this matters

Why this matters

Most Australian property investors know their gross yield. Almost none have modelled what happens to their cash position when vacancy hits 8%, the rate rises 2%, and a major maintenance issue lands in the same quarter. That’s not a worst case scenario. That’s a bad year.

The difference between an investor who survives a bad year and one who is forced to sell at the wrong time is almost always preparation. Not property selection. Not suburb choice. Preparation. Specifically: knowing in advance what your cash reserve needs to be to survive the scenarios that break over-leveraged investors.

This prompt produces the full model in three minutes. Not just the base case you hope for — the bear case you need to plan for, and the survival case you need to be able to fund.

The bear case is the only case that matters before you sign a contract.

What you're building

What you're building

The end result

A three-scenario cash flow model for any Australian investment property. Base case (current assumptions), bear case (rates up 2%, vacancy 8%), and survival case (rates up 3%, rents flat, extended vacancy, one major maintenance event). Annual cash flow, net yield, and cumulative 5-year position for each scenario. The cash reserve required to survive scenarios 2 and 3 without selling.

What you need

Claude (free tier works for this prompt). Your property details: purchase price, configuration, suburb, state. Your finance details: LVR, interest rate, IO or P&I. Your assumptions: weekly rent, management fee, council rates, water, strata if applicable, insurance, vacancy assumption.

Step 01

Paste your property details.Run three scenarios.Read the bear case first.

Paste the prompt below into Claude with your property details filled in. The AI returns three structured scenarios. Always read scenario 3 first — the survival case. If you can’t fund it, you may not be ready to buy.

i.Open Claude at claude.ai. Free tier is fine.Browser
ii.Copy the full prompt below. Replace every bracketed field with your actual numbers.Chat
iii.Send. Three scenario tables return in about 60 seconds.Output
iv.Read scenario 3 (survival case) first. Then read scenario 2. Then scenario 1.Review
Done. Three scenarios, five years each, cash reserve requirement included.
Heads up

The figures in this model are only as good as the inputs you put in. Use your actual expected rent, your actual management fee, and your actual interest rate. Don’t use the agent’s projection for rent — use the median for comparable properties currently available to rent in that suburb.

01
The Prompt

Stress test

Investor cash flow stress test · Claude / ChatGPT · 3-scenario cash flow model

Copy & Paste
Stress test this Australian investment property through three scenarios.

PROPERTY DETAILS: [Address, purchase price, configuration, state]
MY FINANCE: [LVR, interest rate, IO or P&I, term]
ASSUMPTIONS: [Weekly rent, management fee %, council rates, water, strata if any, insurance, vacancy assumption]

Scenario 1 — Base case: current rent, current rate, 3% vacancy
Scenario 2 — Bear case: rents down 5%, rate up 2%, vacancy 8%  
Scenario 3 — Survival case: rents flat, rate up 3%, vacancy 12%, one major maintenance event $8,000

For each scenario show: annual rental income, total outgoings breakdown, net cash flow, net yield, cumulative 5-year position, and cash reserve required to survive.

Flag the point at which I need to fund the property from my own income in scenarios 2 and 3.

Educational analysis only. Not financial advice.
Run it before you sign a contract. Read scenario 3 (survival case) first.
Step 04 · Refine

Your first run is fine. Your fifth is sharp.

Tune 01

Run it with your broker's actual rate

Don't estimate your rate. Get a real quote for investment finance from your broker. The difference between 6.1% and 6.6% changes the holding cost significantly over five years.

Tune 02

Update outgoings figures annually

Council rates, water, and insurance rise. Update the outgoings assumptions in your model annually so your reserve calculation remains accurate.

Tune 03

Test interest-only vs P&I

Run the model under both structures. Interest-only keeps holding costs low but builds no equity. P&I reduces debt but increases monthly cash commitment.

Save it

Save this stress test in your Claude Project. Update the interest rate and outgoings whenever they change. The model tells you if you can keep the property — the market tells you when to sell.

The honest bit

What it still gets wrong.

i.

It doesn't know your tax position

The cash flow in this model is pre-tax. Negative gearing, depreciation schedules, and your marginal tax rate all affect your actual after-tax cash position. Your accountant models the tax layer — this prompt models the cash layer.

ii.

It uses your inputs, not market data

The rent assumption is yours. If you use the agent's projection, the model reflects the agent's projection. Use comparable current listings and recent leases as your benchmark.

iii.

It doesn't model capital growth

This is a cash flow model, not a total returns model. Capital growth is not modelled because it is not guaranteed and cannot be reliably estimated. The model tells you whether you can hold the asset — not what it will be worth.

iv.

Vacancy is always underestimated

Investors consistently use lower vacancy assumptions than their suburb's historical average. Use the suburb's actual vacancy rate from a current source, not a number that makes the model work.

The Workflow

How this stacks.

Day 04 stress-tests the holding costs. Day 05 scans the suburb risks. Day 06 checks your borrowing capacity. Run them together to verify an investment property's viability.

The week three vision

By your fifth deal.

You will know the holding costs of your investments in a down market.

Instead of hoping for capital growth, you'll have modelled an indicative cash reserve for the rate-hike and vacancy scenarios you choose to test. You'll have a clearer view of whether a property looks self-sustaining or looks like a strain on your position. That is the kind of preparation that separates investors who can hold through a down market from those forced to sell — then take the numbers to your broker and accountant.

Coming next
05
Day 05 · live now

Suburb Risk Scanner

Not all suburbs perform the same way — and not all lenders treat them the same way either. This prompt surfaces the supply, demand, employment, and lender appetite signals for any Australian suburb.

Read Day 05