What is fixed interest period and which duration makes sense?

German mortgages typically run with a fixed interest rate for a defined period — the Sollzinsbindung — after which you negotiate a follow-up financing (Anschlussfinanzierung) at whatever market rate exists at that point. Common fixed periods are 5, 10, 15, 20 or 30 years.

Longer fixings generally cost a small interest premium because the bank is taking on more rate risk; shorter fixings start cheaper but leave you exposed to whatever rates look like at refinancing time. There is also a useful piece of German law worth knowing: you can give notice on any fixed-rate mortgage 10 years after full disbursement with a six-month notice period. That means very long fixings aren't actually irreversible — if rates drop significantly, you can exit and refinance.

The right duration usually comes down to three things: the current rate environment (in low-rate periods, locking longer often pays off; in high-rate periods, shorter can make sense), your realistic residence horizon (no point paying the long-fixing premium if you might sell or repay early), and your personal appetite for risk (some people simply sleep better with rate certainty).

For most expat first-time buyers in stable employment, a 10–20 year fixing is a sensible default — long enough to give planning certainty, short enough that you're not overpaying for protection you might not use.