Mieten vs. Kaufen: Why Your Austrian ‘Excel Genius’ Friend Might Be Wrong
Someone in the Austrian finance community built an Excel calculator that claims to finally answer the question: should you rent and invest in ETFs, or buy property? The tool went viral because it supposedly models the true opportunity cost of homeownership. But like most “simple” financial models, it collapses under the weight of Austrian reality.
The calculator’s logic is straightforward: compare two scenarios over 30 years. In one, you take out a mortgage and buy property. In the other, you rent and dump the difference into ETFs. The model assumes identical monthly budgets for both paths, then projects which leaves you wealthier. The creator’s own Austrian-market example shows buying only wins if ETF returns stay below 6.85% annually, well under the MSCI World’s historical average of 10.5%.
The Austrian Tax Trap Nobody Models
Here’s where spreadsheets meet the Finanzamt. The calculator’s creator openly admits it ignores Vorabpauschale, the advance tax on accumulating ETFs that hits Austrian investors every January. This isn’t a rounding error. For a thesaurierender ETF, you’re taxed annually on a fictional “base yield” even if you never sell. The creator suggests subtracting ~1% from expected returns to account for this, but that’s lazy math. The real impact depends on the Basiszins (2.53% in 2025) and your specific ETFs.
Even worse: the model assumes you can freely dip into your ETF portfolio to cover rising rent. In Austria, selling triggers KESt (Kapitalertragssteuer) at 27.5% instantly. The calculator mentions this in the disclaimer but treats portfolio withdrawals as tax-free. For Vienna renters facing 5-7% annual Mietpreissteigerung, that assumption alone makes the entire model suspect.
The Real Cost of Owning in Austria
The community quickly pointed out the model’s soft spot for property costs. One user noted that Betriebskosten (operating costs) for a €450k Viennese apartment often exceed €500/month, higher than some mortgage payments. The calculator lumps these into “laufende Nebenkosten”, but Austrian reality includes:
- Rücklagen for building repairs (legally required minimums often exceed €3/m²)
- Maklerprovision (up to 3% of purchase price, though recent law changes cap this for buyers)
- Grunderwerbsteuer: 3.5% in most Bundesländer, though Lower Austria dropped to 2%
- Eigenmittel: Austrian banks still demand 20-30% equity for non-Geförderte properties
The model assumes constant maintenance costs. It doesn’t account for Vienna’s Altbau stock, where heating alone can hit €300/month in winter due to poor insulation. Nor does it factor in Genossenschaftswohnungen, where you buy shares instead of property, a common Austrian path that exists between renting and owning.
Why Flexibility in Austria Is Worth More Than Excel Shows
The model’s biggest blind spot is the Austrian rental market’s rigidity. The creator assumes you can downsize in retirement, freeing up portfolio cash. But try finding a Mietvertrag for a 50m² apartment in Vienna’s 9th district when you’re 65. The market simply doesn’t work that way. New contracts are routinely 30% more expensive than existing ones due to Richtwertzins limitations that only apply to old leases.
Austrian law favors long-term tenants, which sounds great until you realize it means landlords screen ruthlessly. Without a decades-old contract, you’re paying “Marktmiete”
The Leverage Question
The model assumes you finance the property but compares it to unleveraged ETF investing. This is apples-to-oranges. Austrian real estate’s appeal lies in Kredithebel: you’re controlling a €500k asset with €100k equity. If property values rise 2% annually, your effective return is 10% on invested capital, before accounting for imputed rent.
But leverage cuts both way. The calculator’s creator updated the tool to show break-even points at different ETF returns. At 7% ETF returns (post-tax), renting wins. But that 7% assumes you have the discipline to invest the difference every month for 30 years, a behavioral fantasy. The “disciplining effect of debt”
The 20-25x Rule Still Works
Austrian banks still use the Kaufpreisfaktor as a primary risk metric. If the purchase price exceeds 25x annual cold rent, they flag it as overvalued. In Vienna’s Innere Stadt, you’ll see factors of 35-40x. The calculator’s example uses a 28x factor (€450k purchase vs. €15,600 annual rent), which explains why renting looks better, even before tax complications.
But this ignores Standortwert. A 19th-century Altbau on the Ringstraße isn’t just housing, it’s a Veblen good. You can’t model that with a 7% discount rate.
What Austrian Investors Should Actually Do
The calculator is useful for one thing: showing how sensitive the decision is to your Eigenmittel and tax situation. If you’re a high earner facing 55% marginal tax, the mortgage interest deduction (though limited) combined with KESt-free property appreciation changes the math. If you’re a freelancer with irregular income, the flexibility of renting and investing might outweigh ownership security.
The real answer? Do both. Austrian property markets are inefficient enough that you can find below-market deals, especially through Zwangsversteigerungen or buying directly from elderly owners avoiding Makler. Use those savings to build your ETF portfolio. The calculator’s false dichotomy assumes you’re either all-in on property or all-in on stocks. Austrian wealth has always been built on layered strategies: a purchased Genossenschaftswohnung, a Bausparvertrag, and a steady ETF Sparplan.
Just don’t trust any Excel sheet that claims the answer is a single percentage. The Finanzamt will find a way to make that number meaningless anyway.
