Financing single-family house with granny flat for parents

Don't these considerations with a granny flat come up more often? It always goes similarly:

[*]You only calculate the single-family house
[*]Realize that it doesn't work out financially
[*]Get the idea to additionally build a granny flat
[*]Almost always end up back at point 2

Soon the idea comes up to represent 100k through own work?

These considerations about a granny flat don’t come up that often. It usually goes like this:

[*]You only calculate the single-family house
[*]You realize financially it doesn’t work out
[*]You get the idea to additionally build a granny flat
[*]You almost always end up back at point 2

Is the idea of covering 100k through own work coming soon?

Don’t forget to include the very secure annual profit shares and salary increases for the next twelve years...

You need a tax advisor again... all that for a few hundred EUR per year?

I guess the tax advisor costs at least 600.--/ year. Income tax assistance association half, but in my opinion they are more than correct and only submit what is 150% guaranteed to pass.

I'll do a rough calculation that many will probably comment on as being completely too high or too low, depending on the standpoint. Normal rental yield is 3%. 66% rent is easily manageable even over a longer period, 50% has only recently been allowed and you have to prove the intention to make a profit. You can also offset it with gardening or childcare. This results in a 2% yield for you, from which you can deduct the complete interest expenses (3-4%) and 2% of the construction costs (excluding land) of the granny flat. Ideally, this results in a 4% loss, which you get back on your tax return the following year. Even if you pay 48% income tax, the refund should be well above [150.--/Monat]