How to design a database for a budgeting application?

Question

Fintech

As a pilot project, I am going to develop a simple budgeting application in Django: here is a monthly budget, users plan their expenses and tie them to a particular budget. Here one-to-many communication is simple and clear. But what about actual expenses? Where to submit them? In the same table, just set the 'Fact' property, for example, and use the parent-child relationship? Or still store the actual costs in another table(s)? Then how should the connections between them be organized?
Is there a theory on this issue? Specific solutions (especially Django-related ones) are of course interesting. But here I would like to understand exactly the theory and best practices as it is done in real working applications, so that the embedded data schema would allow further plan-fact analysis.

Answer 1

if there are no unplanned expenses, then put them in the same cell where the planned ones are only in the next field

Answer 2

There is definitely a theory on this. It's called "financial planning and budgeting". And in a narrower sense, "the theory of accounting."
Developing a really good budgeting application is only possible with best practices in financial management, not best practices in database and user interface design.