While making spouse visa application or applying for spouse visa extension UK , ensure that the financial eligibility criteria is fulfilled as laid down by the Home Office. The spouses must have a combined income of at least £18,600 a year. The spouses need not to prove they have extra money if the children are citizens of the EU, Iceland, Liechtenstein, Norway or Switzerland and they do not possess a pre-settled status or are not permanently settled in the UK. You will be asked to furnish documents to prove your income with your application. This could include, saving or joint account statements showing a collective income, last 6 months of payslips or a letter from an employer, dated and on company letterhead. Read More: How much do I need to earn to bring my spouse to the UK?