Four Yield Numbers, One Flat: Why Bruttomietrendite Lies

The same flat, expressed five ways:

One flat. 4.04% and 2.76% differ by a third, and the entire gap is made of things the listing never mentions: €21,500 of Kaufnebenkosten in the denominator, €1,700/year of non-recoverable owner costs in the numerator.

Gross yield is the most-quoted number because it is the only one computable from a listing in three seconds. Its defects, in ascending seriousness:

1. It uses the asking price – an anchor, not a transaction.
2. It ignores 12% of acquisition cost.
3. It ignores every owner cost.
4. It ignores financing. The identical flat is a completely different investment at 4.2% and at 1.2%.
5. It ignores time, so it cannot express "fine at year 12, a disaster at year 4."

It is also blind to the most valuable fact about a tenanted flat: where the sitting rent sits against the ortsübliche Vergleichsmiete. A flat let 20% under the Mietspiegel has embedded upside; one let 15% over it has embedded downside. Identical gross yields, opposite deals. (What you may actually do about that gap is tenancy law – see that track.)

Cash-on-cash has the mirror flaw: it is dominated by your Tilgung choice, which is a savings decision, not a return. Raise Tilgung from 2% to 3% and cash-on-cash gets worse while your net worth grows faster. Never optimise it.

IRR is the only metric that respects time – and it is only as good as its exit assumption, which is 80% of the answer.

Working rule: screen on Faktor, decide on IRR. Gross yield is a cheap filter for rejecting listings in bulk; it is never a reason to buy. When a broker quotes you a yield, ask what is in the denominator. The answer tells you how the rest of the conversation will go.