Borrowing, answered
How do lenders decide how much I can borrow?
Most start from a multiple of income, commonly between four and four and three quarter times, then reduce it for credit commitments and dependants and stress the payment against a higher rate than the one you are offered.
Does a bigger deposit let me borrow more?
Not usually. The deposit sets which rates you can reach rather than the size of the loan, though at a very small deposit some lenders cap the multiple they will allow.
I am self-employed. Is this figure any use?
Treat it as a rough starting point. Lenders assess self-employed income in several different ways, and the same accounts can produce noticeably different answers depending on which method is used.
Is this an agreement in principle?
No. It is arithmetic on the figures you typed. An agreement in principle involves a lender looking at your credit file and your actual circumstances.