I would change the Single Select field into a “Link to another record” and create a new table. You now have a category table linked to you budget entries. You can then use rollup field in the Category table to add up stuff from the Budget table by Linked category.
You could also / instead simply group the records in a grid view and total fields.
Thanks so much - I assume it’s not possible to have a single select field that also links to another record? The single select is a big plus for us, as it makes budget entries way quicker, and stops people entering slightly different things .e.g “Clothes” for one item and “Clothing for another”
No - it’s not - but the Link field works similarly - you just select the ‘category’ from the set of linked records. It’s not quite as pretty as a single select - but you’re then using the ‘relational’ elements of the database to do their thing.