Banks usually want two years of financial statements and tax returns, and many use an average of the two. If your latest year was stronger, some lenders will lean on it; if it was weaker, expect them to use it.
Lenders can add back some non-cash or one-off costs, such as depreciation, to the profit figure. A clear letter from your accountant explaining these makes the application easier to assess.
If you've been trading for less than two years, or your income changed recently, non-bank lenders may accept other evidence such as recent bank statements, usually at a higher cost. Keeping your tax up to date matters either way.