The lender’s research found that more than one in eight employees are expecting a bonus in the next 12 months.
Those aged 25 to 34 are the most likely to expect bonuses in the next year with 18% banking on extra money.
According to the Association of Independent Professionals and the Self-Employed about 1.88 million people work as freelances or contractors.
However Kensington says the numbers of people with so-called complex incomes could be even higher – and it is targeting the mortgage market gap which is growing.
Steve Griffiths, head of sales and distribution at Kensington, said: “Bonuses are widespread throughout the UK workplace and across industries with 13% expecting them to receive them over the next year.
“Once you add the number of people who receive regular overtime, those who work as contractors and even those who have second jobs it is clear that a significant number of potential mortgage customers have more complex income requirements that may require individual assessment.”