There is an order to how Budgyt formulas are calculated and it's useful to know this order before starting to build them.
First of all, there are three types of formula, C2Cs, FOAs, and Rules, and they are calculated in that order - all C2Cs first, then all FOAs, then finally all Rules.
Within each group, the formulas are calculated in order from the top of the screen to the bottom.
In the C2Cs, it is possible to build formulas in the wrong order - i.e. calculating the result of a formula after you have used that result as an input in an earlier formula. If this happens, you will see an error message, and the offending formulas will be outlined in red.
To reorder, click the Reorder button at the top right, and either use the arrows to the right, or drag and drop your formulas to the right place.
FOAs and Rules may not be built in the wrong order, but you can use the same reorder button to move them around to make your list easier to manage.