Forward loan - Secure interest rates now?

That was simply a service. In other words: Because I can.

You are wrong insofar as a 20-year fixed interest rate is refinanced today at a fixed rate. A 5+15 financing will, unless I take other instruments of interest rate risk management into account, only be refinanced in 5 years. This means either additional risk or additional costs for the bank. Both lead to higher conditions.

I meant, what use is a result accurate to one hundredth when countless other factors still play a role and you actually can’t even say within 1-2 tenths where you approximately stand.
That is probably simply the difference between a technician and a "mathematician".
I also wrote that there are probably surcharges, but as said, there are also factors that are cheaper after 10 years (mortgaging, higher salary, etc...).

I meant, what use is a result precise to one hundredth when so many other factors play a role and you can't even really say where you stand within 1-2 tenths.
That's probably just the difference between a technician and a "mathematician."
I also wrote that there are probably surcharges, but as I said, there are also factors that are cheaper after 10 years (loan-to-value ratio, higher salary, etc.)

You are confusing things. For determining the conditions, the loan-to-value ratio of the house, fixed interest period, the bank's risk appetite, and then refinancing as toxi described are decisive. That is what you check now. No one can determine your salary in 15 years, so it is ruled out. All other factors you can determine now or the orientation (risk appetite) is clear. For example, you can discount your property.

And I said "mathematically" because that is the spread given by the forward spread.

If now a bank says, come on, we'll add another 20 points because we are the only ones offering something like that. Then that's how it is. But you can't calculate it, accordingly it's a crystal ball, because the market at this point no longer has enough participants for mass business and is therefore opaque.

The many other factors exist in every business calculation.

We are here on the edge of the usual.

To put it simply: You can also roughly calculate it if you think about it logically. Alternative 1: I take out money today for 15 years, paying e.g. 1.45% per year Alternative 2: I take out money today for 5 years (0.75%) and already arrange the follow-up financing in 5 years for 10 years. Then the total term is also 15 years.

Both alternatives have the same interest and capital commitment and must lead to the same total interest expense over the entire period. Financially, it is calculated a little differently in detail, but to put it simply:

15 * 1.45% = 5 * 0.75% + 10 * X. Then X would be 1.8%, i.e., your rough forward rate for a loan in 5 years for then 10 years term. That would be roughly a surcharge of 0.80% compared to a current 10-year loan!

Financially exact calculation cannot be explained here briefly, but the approximation above is already quite good on a very flat interest rate curve and can be solved with a simple calculator.

Aside from that, I understand your concerns. The Bund futures, which is an early warning indicator for interest rate development, has known only one direction since 09/28: downwards. And that means in reverse that interest rates will first rise. Not much, that is not economically feasible, but for the individual it can still be a lot of money.

Well, the Bund futures initially only express an expectation. Moreover, German and European politics over the past years have shown that the interest rate decision is not primarily dependent on German interests. Although the Bund futures are not uninteresting, they do not seem to me to be the most important indicator. I think significant interest rate changes in Europe will only occur if either the ECB's monetary policy objectives are achieved (which I currently do not see) or the USA takes substantial interest rate steps, leaving the ECB no choice but to follow (with a delay). Otherwise, the consequence would be a massive capital outflow to the USA. The British have just lowered interest rates, and Switzerland and Sweden have negative interest rates. There is still potential for the ECB to go downwards. In fact, mortgage loans have become somewhat more expensive because the yield on government bonds has risen.