Lenders calculate your affordability by looking at your income. Most lenders do this by looking at your last three year’s trading history. But specialist lenders will consider you with less than three year’s accounts.
Lenders each have different lending criteria which will affect how much they’re willing to lend to you as a sole trader, so the calculations will vary, but on average lenders will be willing to give you up to 4.5x your income amount. Some lenders will give you more than that, some will offer less depending on your situation and what their criteria is.
Generally, the amount they’ll be willing to loan a sole trader on a mortgage will be calculated like this:
The max loan amount = (net profit, or, total income received) x 4.5