Most lenders treat commission income as variable, which means a single recent paystub won't tell the full story. Instead, underwriters look at a two-year history to determine whether the income is stable and likely to continue. The goal is to filter out one-time spikes or short-term surges that might not repeat. A borrower who earned a large commission last quarter but has averaged modest earnings over the past two years will typically be qualified on the lower figure. This conservative approach protects both the lender and the borrower from taking on a payment that becomes unaffordable when income dips.

The actual calculation usually starts with the borrower's tax returns, specifically the IRS forms that report self-employment or commission earnings. Lenders add back certain deductions that reduced taxable income but don't reflect actual cash flow, such as depreciation or recurring business expenses that aren't tied to ongoing operations. After those adjustments, the resulting figure is divided across the relevant period to produce a monthly qualifying income. For W-2 employees who earn commissions on top of a base salary, lenders often blend the base salary with the averaged commission to arrive at a total qualifying figure. Borrowers who take large deductions to lower their tax bill may find that their qualifying income is smaller than their actual take-home pay.

Documentation matters more for commission earners than for almost any other borrower type. Underwriters typically request two years of personal tax returns, recent paystubs covering at least 30 days, and a written verification of employment. Self-employed commission earners may also need a year-to-date profit and loss statement and, in some cases, a balance sheet. Keeping clean books, minimizing unnecessary deductions in the years leading up to a home purchase, and maintaining consistent earnings can all make the process smoother. Borrowers who anticipate a mortgage application in the next year or two should talk to their accountant about how to position their income strategically.