Property investment
A property changes over decades: rent rises, remaining debt falls and tax benefits expire. A snapshot is not enough to judge the full holding period.
Remaining debt
With an amortising loan, the monthly payment usually stays constant during the fixed-rate period, but its composition changes. At the beginning, most of the payment is interest. As the balance falls, the principal share rises steadily. Over 30 years, this accelerates equity building in the second half of the term.
Rent growth & inflation
Loan payments often stay fixed during the rate period, while rent and operating costs generally move with inflation. Monthly cash flow can therefore improve over time even when the payment is unchanged. A model based only on the first year can understate long-term economics.
Taxes & depreciation
Through tax depreciation (AfA), part of the building value, not the land value, can be deducted over its useful life. This can reduce taxable rental income and directly affect after-tax cash flow, especially in the early years when interest is still high and deductible.
Combining depreciation and interest can make the property show a tax loss in the early years even when the real cash flow is positive. That is one reason property investments can look attractive from a tax perspective.
Exit analysis
An exit analysis estimates what remains at a chosen sale date. It calculates an expected sale price from an assumed appreciation rate, subtracts the remaining loan balance and, for a holding period below ten years, includes the relevant German speculation tax on the gain.
Total return comes from the cash flow during the holding period plus the net sale proceeds.
Cash flow and wealth
Cash flow shows how much money remains in your account each month. Principal repayment is part of the monthly burden, but it does not simply disappear: every repayment reduces the loan balance and increases your equity. Answer two questions separately: how much must I contribute each month, and how much wealth is created through repayment?
For example, suppose €150 remains after rent, operating costs and interest while you repay another €350. The cash flow is €150 minus €350, or a €200 contribution. At the same time, the balance falls by €350. That is a liquidity burden and a separate wealth-building component.
Assumptions
The final chart can look precise even though it is built from assumptions. A different annual rent-growth rate can materially change cash flow after many years. The same applies to maintenance. A calm first decade does not tell you whether the roof, heating system or facade will need funding later.
I would never look at one curve only. Conservative rent, higher costs and a higher refinancing rate often tell you more than an optimistic base case.
Model boundary
The model can show how your assumptions interact. It cannot know when a major repair arrives, how the location develops or which price you will achieve at sale. The exit analysis is therefore only as good as its sale-price and cost assumptions.
The projection becomes useful when you compare it with reality regularly. After each year, enter actual rent, costs, remaining debt and interest paid. You will quickly see whether the original plan still holds or an assumption needs to change.
Decision
The strength of a 30-year model is not that it knows the year 2046. It shows when the plan is most sensitive. Cash flow may be tight at first while debt falls quickly. A property may look good until refinancing becomes expensive. Or most of the result may come from the sale. A simple annual return would hide these points.
Compare more than the final value: the lowest liquidity reserve, refinancing date, cumulative contributions and the share of the result coming from the exit. If almost all profit appears at sale, your decision depends more on the final market price. If the property remains viable without strong appreciation, the risk profile is different.
Enter rent growth, financing and tax parameters, then simulate cash flow, remaining debt and exit value over 30 years.
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