Invoicing can be a good way to prove your income, as long as you are invoicing thoroughly and accurately. You will need to provide an invoice and show that it is paid for in order to count it as income. If you can trace that invoice payment back to a line on your business account, you will find that it provides more proof than before. In the case of providing a product or service to the customer, it is necessary for you to provide an invoice to the client. This should include as many details about the project as possible including the time you spent on the project and how much they owe you. This invoice is going to serve as a proof of income for you and a proof of expense for them if they need it. There are different things that you should include on the invoice to make it more official. This includes: The business name and address details. The name and the address of the company you plan to invoice A unique invoice reference number that goes just to this invoice and makes things easier. A date on the invoice. A list of the services or products that you provided to them as well as the cost of each. The total amount of the invoice The terms for paying the invoice If you can add other information like any telephone and fax numbers and the company email address, this can help as well. It is always best to have more information rather than less to keep things safe here.