MLH07,
Don't confuse a very simple situation.
The bank statement will show income and most outgoing expenditure.
If you are generally living within your means and can afford the cost of another adult consumer joining the household, this will be immediately obvious to the ECO.
People earning very low amounts that leave them with a discretionary income close or equal to the equivalent of means-tested benefit or have experienced recent "one-off" expenses (such as weddings/visa fee's etc) might feel the need to make a simple budget plan to signpost how they can afford another person in the house.
With regards to your income, there's really only so much you need to demonstrate, if you really feel the need to explain and show how you meet the rules then there is possibly less chance of refusal.
But just be careful that you do not include too much information or that you make the explanations/budget plans over complicated.
ECO's are under time pressure and performance targets just like we all are.
A couple (both aged 18 or over) need to show around £106 disposable income per week
Each dependent child (from birth to day before 20) requires around £62.33 additional disposable income per week
This is based on current income support levels.
In principle disposable income is the amount of money left after payment of any key fixed/regular expenditure (such as rent or mortgage payments etc)
We all have different key fixed/regular outgoings.
