How a Bank Statement Mortgage Calculator Sizes Your Qualifying Income

The Quick Read: A bank statement calculator takes the eligible deposits from your statements, subtracts an expense factor, and divides by the number of months to produce one monthly income figure. That number is only an estimate. The lender’s final figure depends on which deposits it excludes, which expense factor it applies, and how much of the business you own.

• Qualifying income equals eligible deposits, times one minus the expense factor, divided by months.
• Documentation is typically 12 months of personal or business statements, subject to lender guidelines.
• Transfers, loan proceeds and refunds usually come out before the math starts.
• A documented expense factor can raise the counted income on identical deposits.
• A calculator output is an estimate, not an approval.

Self-employed investors often look underpaid on paper. Write-offs shrink taxable income, and a lender reading traditional personal-income documentation sees the smaller number. Bank statement programs read your deposits instead. This guide walks through exactly how that conversion works, where it breaks, and how to use a calculator without fooling yourself.

Key Terms Defined

Eligible deposits: Money that came in from real business or personal income, after transfers, loan proceeds and refunds are removed.

Expense factor: The share of business deposits the lender treats as operating costs and does not count as your income.

Ownership share: The percentage of the business you own. Credit is generally given only for your share.

Lookback period: The number of consecutive months of statements the lender averages, commonly 12 and sometimes 24.

Qualifying income: The single monthly income figure the lender uses to weigh you against your debts.

Debt-to-income ratio (DTI): Your monthly obligations divided by your qualifying income.

What Is the Formula, Step by Step?

The formula is eligible deposits multiplied by one minus the expense factor, divided by the number of months. Each step below shows where a calculator makes an assumption on your behalf. Across the wholesale network Lendmire works with, the sequence is consistent even though the specific factors differ by lender.

1. Pick the window. Most programs we place files with ask for 12 months of consecutive, complete statements. Some lenders offer 24 months, which Scotsman Guide also describes as a standard option.

2. Pick the account type. Business, personal or a mix. The choice changes how much of each deposit counts.

3. Total the eligible deposits. Strip out transfers between your own accounts, loan proceeds, refunds and anything the lender cannot tie to income.

4. Apply the expense factor to business deposits. Scotsman Guide uses 50% as its example of a standard factor. That is an illustration, not a rule. Factors vary by lender and program, and personal-account programs may haircut deposits very little.

5. Swap in a documented factor if the program allows it. A profit-and-loss statement or an expense statement from a third-party tax professional can sometimes replace the flat factor, as the same Scotsman Guide piece notes. You cannot self-certify one. The lender decides whether to accept it.

6. Prorate by ownership. A 60% owner generally counts 60% of the result.

7. Weigh the result against your debts. The finished income number goes into the DTI test alongside your other obligations and the new housing payment.

Why the Expense Factor Moves the Number So Much

The expense factor is the biggest single lever in the calculation, because it applies to every deposit at once. Take deposits that average 100 units a month. A flat 50% factor counts 50 units. A documented 30% factor counts 70 units. That is 40% more qualifying income from identical bank activity. This is simple arithmetic for illustration, not a market statistic.

The table shows why you should ask any lender for its factor in writing. For a deeper look at how factors are set, see Lendmire’s piece How the Expense Factor Shapes Income on a Bank Statement Mortgage.

Which Deposits Actually Count?

Only deposits that look like repeatable income count. A calculator cannot judge this for you, so you do the triage before you type anything in.

Commingled accounts need attention. If personal and business money share one account, the factor generally applies only to the business portion, so separating them helps. Contractors who pass subcontractor payments straight through should expect scrutiny.

Should You Run 12 Months or 24?

Run both when you have the statements, then see which story your deposits tell. Twelve months fits a business that grew recently, because the strong year is not diluted by a weaker one. Twenty-four months helps when income is seasonal or lumpy, since a longer window smooths spikes and long off-seasons. If deposits are falling, the shorter window is the one a lender may find harder to like, and the calculator’s simple average will hide the slide.

Programs in Lendmire’s network are built around 12 months of statements, and window length follows each lender’s program sheet. A calculator that asks for 24 months may be modeling a different program than the one you end up in.

When the Simple Average Misleads

A calculator averages. An underwriter reads the trend. Three situations expose the gap.

Rising deposits. The average understates where you are now, and the lender may use the average anyway.

Falling deposits. The average overstates where you are heading. Expect questions.

Missing months. One skipped statement distorts the average and often makes the calculator’s output unreliable. Lenders generally want a full, consecutive window.

A business under 24 months old is a different case. Underwriters tend to weigh credit quality and liquid assets more heavily next to a short history, subject to the program.

From Income to What You Can Borrow

Qualifying income is the front half of the story. The back half is your debt load, plus the reserves and credit the file carries. Under the federal ability-to-repay rule at 12 CFR 1026.43, a creditor must verify the income or assets it relies on, and the CFPB’s compliance guide notes that debts and mortgage-related obligations such as taxes and insurance are part of the picture. The rule does not hand lenders a formula. Expense factors and deposit rules are program guidelines, which is why results differ between lenders.

The leverage and size ranges below are typical on the programs we see, subject to lender guidelines and credit:

• Primary residence purchase or rate-term: up to 90% LTV, with the strongest files earning the top of the range.
• Owner-occupied cash-out (primary or second home): up to 80% LTV with a fixed expense ratio, or 75% with an accountant-prepared ratio, depending on loan size and credit.
• Investment property cash-out: tops out around 75% LTV. Investment purchase leverage on bank statement documentation varies by lender.
• Asset-depletion alternative: up to about 80% LTV on a primary residence.
• Loan amounts: roughly $125,000 to $3,500,000, with reserves commonly around six months of the housing payment.

Occupancy also decides the paperwork. An owner-occupied file is a consumer mortgage. A bank statement loan on a non-owner-occupied rental, including a short-term rental, is business-purpose and exempt from TRID. Consumer mortgage licensing for this lane covers 16 states. Term length follows individual lender program sheets.

Bank Statement or DSCR? A Decision for Investors

If your personal income is strong and your debts are light, bank statements can work. If your portfolio is large or held in LLCs, you may do better qualifying on the property side instead. A DSCR loan is reviewed primarily on property-level rental income covering the payment, subject to lender guidelines, and it ignores your personal deposits. Bank statement programs still count your other liabilities, so the two paths fit different files. Lendmire’s complete DSCR loans guide lays out when the property-income route fits better.

One more point on K-1 earners: if part of your income arrives that way, the lookback question gets its own wrinkles, covered in Lendmire’s article Does K-1 Income Favor 24 Months on a Bank Statement Mortgage?.

Why the Calculator and the Underwriter Disagree

The tool’s number and the lender’s number diverge for predictable reasons.

• The calculator assumed a factor the lender does not use.
• The lender screened out deposits you counted.
• Ownership share was left at 100%.
• The window or account type differed from the program.
• A trend review or missing month changed the average.
• Credit, reserves, property and DTI still have to clear.

The tool is an illustrative estimate. Treat it like a fitting-room mirror: useful, and not the final purchase.

Before You Run the Numbers

• Collect every statement in the window, complete and consecutive.
• Mark transfers, refunds and loan proceeds in advance.
• Write a short explanation for any large one-time deposit.
• Separate personal and business money where you can.
• Know your ownership percentage.
• Ask your accountant whether a prepared expense statement is available.

Tax treatment can depend on how the funds are used and how the property is held; investors should keep clear records and speak with a qualified tax professional before relying on any deduction.

A file is reviewed on documented income under the applicable program, subject to lender guidelines. This is not a commitment to lend.

About Lendmire

Lendmire (NMLS# 2371349), a non-QM mortgage broker serving investors in 41 markets including Washington, D.C., helps structure DSCR scenarios commonly evaluated around a property’s rental income rather than personal income paperwork, subject to lender guidelines. A Scotsman Guide Top Mortgage Workplace in 2025 and 2026, Lendmire places loans through wholesale investor lenders and is not a direct lender.

References

1. Scotsman Guide, Rev Up the Engine for Non-QM Lending

2. eCFR, 12 CFR 1026.43

3. CFPB ability-to-repay and qualified mortgage compliance guide