Hello Lucy,
I think we need to get some information about all these KfW programs... is there anything where you can read an overview?
6Richtige gave you a link, a good first approach.
Nevertheless, financing is a sensitive matter that should always be tailored to the personal situation; you can’t just learn that as an outsider to the industry. That’s why I advise you to have a conversation – besides your bank – also with an independent financing broker; house banks rarely look beyond the obvious. It will cost you about 2 hours of your time, but afterwards you will know exactly what is possible and what is less advisable. A low interest rate is not always the be-all and end-all in an investment, such as building a single-family house. Often it is a combination of many things; sometimes – in the long run – a program with a slightly higher interest rate can be the better solution. For this, however, you must be open with your bank or the independent financing broker and provide them with all relevant data. Then a viable financing will work out, where the remaining net income can also absorb a setback, for example in the form of a broken washing machine.
Best regards