When you apply for a mortgage, the lender doesn't just look at last month's paycheck or last year's tax return. Instead, underwriting guidelines call for a two-year lookback and an average of qualifying income across that period. That rule applies whether you're a W-2 employee with overtime and bonus pay, a commissioned salesperson, a self-employed borrower, or a landlord reporting rental income.
Why 24 months
The two-year window exists to measure stability. A single strong year could be an anomaly—a one-time project bonus, an unusually busy sales quarter, or a year when a rental property had no vacancy. By averaging 24 months of income, underwriters smooth out volatility and arrive at a figure they can reasonably expect to continue. The lookback also aligns with the fact that most borrowers provide two years of tax returns and two years of W-2s during documentation.
How the average is calculated
For W-2 income that includes variable components like overtime, bonuses, or commissions, the underwriter adds the total from each of the past two years, divides by 24, and arrives at a monthly average. If you earned $80,000 in year one and $92,000 in year two, the average is $86,000 annually, or about $7,167 per month. For self-employed borrowers, the calculation starts with adjusted gross income or net profit from Schedule C or partnership K-1s, adds back certain non-cash deductions like depreciation, then divides the two-year total by 24. Rental income follows a similar pattern, netting rent against expenses on Schedule E and averaging the result.
When the trend is declining
If income is falling—year two is materially lower than year one—many lenders will use only the most recent 12 months instead of the full 24-month average, because the higher historical figure no longer reflects current earning power. That shorter calculation protects the lender and the borrower from an overstated qualification. Conversely, if income is rising, the 24-month average still governs; your recent higher earnings do not override the blend unless you can document a permanent change, such as a promotion with a new base salary that has been in effect for a defined period.
The Alliance take
Understanding the two-year lookback helps you set realistic expectations before you start an application. If you switched from a salaried role to commission work six months ago and your new income is higher, that increase probably won't be fully recognized yet. If you launched a business last year and showed a loss in year one but strong profit in year two, the average may still be modest. The rule rewards consistency. Gather 24 months of documentation early, and if your income picture is complex—multiple jobs, recent self-employment, or a rental portfolio—expect the underwriter to build that average line by line from your tax transcripts and pay stubs.
Consult a CPA or attorney; this is not tax or legal advice.