When you have calculated your expected expenses and income, the next step is to write your budget down in a way that is useful for the organisation and for funders.
For the organisation’s own use it should be possible to understand, at any time, how amounts were decided upon and what they are.
Motivations for particular items in the budget do not have to be written into the budget, but they can be part of the written proposal, or they can be attached to the budget as notes.
Where you think that something in the budget may be unclear to the reader, it is worth including a note to explain it. For example, when in the first year of the budget you have a fairly small amount, but in the second year it is much bigger, you should have a note explaining the big increase.