A common and recurring question is: What should I keep in my Zettelkasten?¹ Should I include any and all pieces of information, including bank statements and things to do?

With the caveat that this distinction between what does or doesn’t belong in your Zettelkasten will (and should) be different for everyone, I want to share my opinion on the matter.

I reserve my ZK for those bits of knowledge that are of intellectual relevance to me – either because they are interesting, because they relate to my intellectual endeavours, or because it is information that I want to return to on an intellectual rather than a practical level.

Relatedly, I try to put information in there that is of "timeless" relevance, so to speak – so no plans, todo’s or lists of books to read. All that stuff, including the practical information you refer to, I store elsewhere. (On a sidenote: this doesn’t mean that your notes shouldn’t change. To the contrary, notes should very much be "living things", continuously being reworked and expanded upon.)

The important thing is this: when I browse through my notes, I want to find and encounter stuff that feels valuable according to the characteristics I mentioned above. All the rest, all of the practical stuff, simply feels like clutter.

A different way to convey this: consider your ZK as a communication partner that you can have a conversation with. Do you want to talk about bills and plans? Or do you want to talk about ideas and concepts?