Financing the purchase of a single-family home: Lower interest rate or longer term?

Among them is also our best offer so far. Unfortunately, our terms are not as good as yours ;-)

Clearly 15 years. Why? Because you repay more quickly and the residual risk after 15 years is manageable with the remaining debt. If you want more security, then take 20 years. But I don't see any reason for that. Even then, there are still almost €90k left at the end of the fixed interest period. That is "only" €55k less than after 15 years. However, you have accepted higher interest rates for a marginally smaller remaining debt.

In my opinion, you have to set the rate equally in both variants for a true comparison. If your offer is as detailed as ours, then you can also read off the remaining debt after 15 years for the 20-year offer. For me, that is the 'real/correct' comparison: Is it worth an additional X € remaining debt to have an interest rate lock for 5 more years? We ended up with a surprisingly low amount (I even asked specifically if there had been a calculation error), so we definitely tend towards 20 years.

Very simplified: 0.25% * €400,000 makes €1,000 per year difference, which you save or could pay off accordingly more. I think it's worth it. Is the 5-year longer fixed interest period worth €1,000 per year? If interest rates remain low, the special termination will come anyway in 10 years, and then you will have spent all the money for nothing.

I would take the 20-year fixed rate. But I am also looking for security in this regard. Who knows how high the interest rates will be in 10 or 15 years. At least 10 years ago, they were significantly higher than they are today.

The numbers are not correct at all.
For the 15er, the remaining debt is lower, theoretical term 22Y8M. After that, the APP crashed... :rolleyes: