Bank Statement Loan Expense Factors: How Lenders Haircut Business Deposits

The short version

Lenders assume a 50% expense factor unless a CPA letter or P&L proves otherwise. Low overhead businesses gain the most from a CPA letter.

Dane’s take

A good CPA letter can change your buying power more than a rate change can.

Under CFPB Regulation Z (12 CFR § 1026.43(c)), mortgage lenders can't assume that every dollar deposited into a commercial bank account represents personal income. Running a business requires capital: rent, payroll, software, raw materials, inventory, insurance, and equipment.

To satisfy the federal Ability to Repay (ATR) requirement without reviewing tax returns, Non QM underwriters apply an expense factor (also called an expense ratio). The expense factor is the percentage of gross deposits subtracted to account for operational overhead. The remaining amount represents qualifying personal income.

How this expense factor is calculated will determine your approved loan amount.

The default 50% underwriting rule

Across the Non QM secondary mortgage market, the baseline starting point for business bank statement loans is a fixed 50% expense factor.

Under this rule, underwriters assume that for every $100,000 deposited into your business operating accounts, $50,000 pays for business overhead, and $50,000 is available for personal debt service.

The default 50% rule is attractive for businesses with high overhead:

• If you operate a physical manufacturing plant, restaurant, retail store, or transportation company where actual operational expenses, cost of goods sold, and payroll run at 70% to 80% of revenue, the lender’s 50% assumption works in your favor.
• That means the standard factor can work in your favor when your real costs are higher than 50%.

However, for modern service oriented, technology, consulting, or advisory practices, a 50% blanket haircut can reduce qualifying income well below economic reality.

How underwriters adjust expense factors

When a 50% haircut reduces qualifying income too much, Non QM guidelines provide three primary methodologies to document lower actual overhead:

Method 1: Standard Investor Default

Gross Deposits × 50% Net Margin = Qualifying Income

(No independent accountant documentation required)

Method 2: CPA / Enrolled Agent Attestation Letter

CPA confirms business structure, employee count, and certifies an expense ratio (for example, 20%)

Gross Deposits × (100%, CPA Ratio%) = Qualifying Income

Method 3: CPA Prepared or Reviewed P&L Statement

12- or 24 Month Profit & Loss prepared by an independent tax professional

Underwriter cross references bank deposits against P&L gross revenue within a 5% to 10% tolerance

Method 1: the default 50% ratio

No third party accounting documentation is required. The underwriter sums the eligible deposits across 12 or 24 months, divides by the number of months, multiplies by 50%, and applies the borrower's ownership percentage.

Method 2: the CPA / enrolled agent attestation letter

You provide a formal attestation letter from an independent, licensed CPA or Enrolled Agent (EA). The letter must state:

• That the CPA or EA has prepared tax filings or reviewed the accounting records for at least two years.
• The exact nature of the business and its operational model.
• The number of employees (or confirmation of zero employees).
• A specific estimated operating expense percentage (for example, 15%, 25%, or 35%).

Many Non QM investors set an absolute floor on CPA letters, commonly capping minimum allowable expenses at 10% to 20%, regardless of whether the CPA claims overhead is lower.

Method 3: third party prepared profit & loss (P&L) statement

You submit a 12- or 24 month P&L prepared, signed, or reviewed by a licensed third party tax professional.

Underwriters verify the P&L through a deposit reconciliation test:

• The underwriter totals the eligible deposits from the bank statements over the same period.
• The bank deposits must match the gross revenue reported on the P&L within a strict variance threshold (typically within 5% to 10%).
• If deposits align, the underwriter relies on the net profit margin established on the P&L rather than the 50% default.

Industry margin variations: why overhead matters

Non QM underwriters review your industry classification (NAICS code) and corporate footprint. If an applicant presents a CPA letter claiming a 15% expense factor, the underwriter evaluates whether that figure aligns with standard operating requirements for the sector.

Underwriters reject unrealistic CPA letters. If a CPA signs a letter asserting that a commercial roofing company with six commercial vehicles and fifteen employees operates at a 15% expense ratio, the underwriter will reject the letter as unreasonable and revert to the 50% default or decline the file.

What makes a CPA letter legally and operationally valid?

Mortgage brokers and CPAs often run into conflicts over the wording of expense letters. Because CPAs face professional liability risks under American Institute of Certified Public Accountants (AICPA) standards, many accountants refuse to certify or guarantee future business profitability. Underwriters don't require an audit level guarantee, but they do require clear operational statements.

An acceptable CPA expense letter should contain:

• The CPA or EA's active state license number and verification details.
• The legal name of the business entity and the borrower's exact ownership share.
• A clear statement regarding the business profile: "The company provides remote software architecture consulting. The company has zero W2 employees, owns no commercial real estate, leases no capital equipment, and incurs minimal travel expenses."
• A specific expense factor range or cap: "Based on my review of the business operational records, the operating expense ratio doesn't exceed 20% of gross revenue."

If your CPA includes broad liability disclaimers stating that the letter was prepared without independent verification and can't be relied upon by third parties, the underwriter’s compliance department may reject the document. Discuss the template with your mortgage professional before asking your CPA to draft it.

Mathematical model: how the expense factor changes purchasing power

The following scenario shows how different expense factors impact borrowing capacity for a business generating $80,000 in monthly gross bank deposits ($960,000 annually) with a 100% owner.

• Assumed Personal Monthly Debt Obligations: $1,500 (auto loan, credit cards).
• Maximum Allowable DTI: 45%.
• Mortgage Rate Example: Illustrative 7.00% 30 year fixed term.

In Case B, lowering the expense factor from 50% to 25% with an accountant letter increases qualifying monthly income by $20,000, adding over $1,000,000 in supported mortgage capacity. In Case C, a business with heavy real costs gets the same result as Case A. The 50% factor is the lender's fixed rule, so a CPA letter wouldn't help here.

Audit triggers: when underwriters challenge the ratio

Even when a clean CPA letter is provided, an underwriter will cross examine the bank statement transaction details:

• Visible Payroll Inflows and Outflows: If the bank statements show large, recurring disbursements to payroll processors (such as ADP, Gusto, or Paychex) that account for 40% of all monthly deposits, a CPA letter asserting a 20% expense ratio will be rejected immediately.
• Large Vendor Wires: If substantial outgoing wires to suppliers consume most incoming deposits, the underwriter will challenge a low expense ratio.
• Cash Flow Squeezes: If the account ending balance declines steadily over consecutive months, underwriters may conclude that actual operating expenses exceed incoming revenue, requiring an expanded audit.

Review your statements with your mortgage broker before selecting an expense documentation strategy. When your actual business overhead is low, defend it with a compliant CPA letter. When your overhead is high, take advantage of the standard 50% default.