My question is this
Why are you asking that question?

Where does the application form ask that?

In terms of Financial Requirement you MUST either meet the stipulated gross income of £18,600 per year for a couple OR you must qualify for the exemption.

In meeting the Financial Requirement of £18,600 there is no requirement to analyse 'affordability'. UKBA do not require a budget sheet showing living expenses. Period.

If going the exemption route you must show a NET INCOME (after Total housings costs and PAYE deduction) of £111.45 per week per couple (valid until April 5)

John, I very kindly suggest you stay focussed on what's required for your specific case.

Why not study the VAF 4A (December 2012) application forms:-

Personal Details Form - Partner Settlement (spouse visa)

Appendix 2- Financial Requirement Form

Guidance Notes