Bank Statement Income Averaging Rules for 12 vs. 24 Months

The Quick Read: Neither window is better across the board; the right one depends on whether your deposits are rising, flat, or seasonal. A 12-month window reflects recent strength, while a 24-month window smooths dips and peaks across two full years. Lenders set their own lookback, so the practical move is to run both calculations and see which one a given program will accept.

• A 12-month average uses only the latest year of eligible deposits, so growth shows up fully.
• A 24-month average spreads income over two years, which steadies seasonal or lumpy files.
• Declining income hurts under either window, and switching windows does not hide it.
• Business accounts take an expense factor; personal accounts usually count more of each deposit.
• On a rental purchase, DSCR financing often replaces this whole exercise.

Side-by-Side

The table below compares the two lookback styles on file mechanics. The 24-month column shows published industry norms, which vary by lender. The 12-month column reflects the documentation basis across the programs Lendmire’s wholesale network places.

Qualification on either path happens on documented income under the applicable program, subject to lender guidelines.

How the Averaging Works

The formula is the same in both windows. The underwriter totals eligible deposits, applies an expense factor if the account is a business account, and divides by the number of months. Twelve months divides by 12. Twenty-four divides by 24. That’s the entire structural difference.

No federal rule picks the window. The CFPB’s Ability-to-Repay compliance guide requires a lender to verify the income or assets it relies on with reliable third-party records, such as bank statements. It doesn’t say how many months. Lookback length, expense-factor defaults, and documentation standards are program design set by each lender and investor. Across a wholesale network, that means the same borrower can see different treatment from one program sheet to the next.

On a working file, the steps look like this:

1. Confirm the account belongs to the borrower or the borrower’s business.

2. Check that statements are complete, with every page and no gaps.

3. Identify the source of each deposit.

4. Pull out ineligible deposits.

5. Look at overdrafts, returned items, and unusual transfers.

6. Total what remains.

7. Apply the expense factor on business accounts.

8. Divide by 12 or 24.

Underwriters may also ask for invoices, contracts, a profit-and-loss statement, or a letter from a tax professional.

Key Terms Defined

Lookback window: The number of months of statements the lender averages to set income.

Eligible deposit: A deposit the underwriter accepts as income from the borrower’s work or business.

Expense factor: The share of business-account deposits the lender treats as operating cost, set by the lender and not chosen by the borrower.

Qualifying income: The monthly figure left after exclusions, expense factor, and ownership share.

Ownership share: The borrower’s percentage of the business, which scales the income counted.

What Counts and What Doesn’t

Transfers between your own accounts, loan proceeds, gifts, and one-time windfalls are typically excluded. Large deposits with no documented source are the most common file-stopper. An underwriter can’t count what it can’t trace.

Commingling causes the next most common problem. When personal and business money mix in one account, the underwriter has to sort it by hand, and the file slows down on conditions. Keep business deposits in a business account and document any second income stream on its own.

Rent deposits need care too. Rental receipts generally aren’t treated as business revenue for expense-factor purposes, and programs differ on how they handle them. Ask the program sheet, not the borrower’s assumption.

When 12 Months Is the Better Fit

Choose the 12-month window when income is climbing. Picture a contractor whose latest year of deposits runs well above the year before. A 12-month average counts the full recent strength. A 24-month average pulls in the lighter year and lowers the number, which can shrink the maximum loan size. The exact numbers vary by lender and program and follow a full review of property, leverage, and credit.

It also fits when months 13 through 24 were a weak stretch, such as a slow year, a medical leave, or a business restart. The older months simply fall outside the window.

The documentation burden is lighter too. Twelve months of statements is the baseline across the programs Lendmire’s network places, and fewer statements means fewer chances for a stray deposit to trigger a condition.

The catch: a 12-month window that happens to catch only the busy season can overstate income. Underwriters look at trend and seasonality, so a spike won’t carry the file by itself.

When 24 Months Is the Better Fit

Choose 24 months when income is steady, seasonal, or lumpy. A landscaper or short-term-rental cleaner with heavy summers and thin winters looks very different in any single year, depending on where the window starts. Two years of deposits show the true annual pattern, and lenders tend to read that as more stable.

It also helps when months 13 through 24 were the stronger stretch. A big project two years back lifts a 24-month average above what the latest 12 months alone would show.

The cost is documentation and drag. Twenty-four statements means twice the pages to screen, and a weak recent stretch pulls the average down, or a strong recent stretch gets diluted. Not ideal for fast-growing files.

Here’s the practical read: the pattern decides, not a rule that longer is safer. Run both windows, apply the expense factor to each, and compare. Many loan officers use whichever result the program accepts and that serves the borrower better.

Edge Cases That Move the Number

Declining income. A 24-month average can mask a downward trend, but underwriters apply declining-income scrutiny, so the higher calculation may not be accepted automatically. Moving to 12 months doesn’t fix it either. The trend is the problem.

Business under two years old. A 24-month program can’t be used when the history doesn’t exist. This pushes younger businesses toward the 12-month path.

Missing months or account changes. Gaps in statements stall files. If you changed banks, line up both sets with no break between them.

Expense factor documentation. Some programs allow a lower factor when a CPA documents actual expenses, and the letter should cover the same period as the statements. Owner-occupied cash-out can use a fixed expense ratio, and an accountant-prepared ratio may be accepted in its place.

Ownership percentage. Income is multiplied by your share of the business. A 50% owner counts half.

Single spikes and dips. One large contract moves a 12-month average more than a 24-month one, because it sits on a smaller base. Underwriters notice this and may ask for contracts or invoices.

Where the Window Matters for Investors

For a rental purchase, the question often disappears. DSCR financing qualifies primarily on property-level rental income covering the payment, subject to lender guidelines, so personal deposits don’t set the loan. Lendmire’s bank statement mortgage loans for self employed covers how investors often use bank statements for a primary residence and DSCR for rentals. The complete DSCR loans guide explains how the rental side works.

The window matters when the property is owner-occupied, meaning a primary residence or second home. Those files are consumer mortgages, and TRID disclosure applies. A bank statement loan on a non-owner-occupied rental, including a short-term rental, is business-purpose and exempt from TRID. The regulatory basis for that split is Regulation Z’s business-purpose exemption, and the test looks at the loan’s purpose, not just the property label.

Leverage depends on the transaction. On a primary residence purchase or rate-term refinance, select lenders in the network go up to 90% LTV on bank statement income, with the top of the range reserved for stronger files. Owner-occupied cash-out runs up to 80% LTV with a fixed expense ratio. Investment-property cash-out tops out around 75% LTV. Investment purchase leverage on bank statements varies by lender. Loan sizes run roughly $125,000 to $3,500,000, with reserves commonly around 6 months of the housing payment. Everything is subject to lender guidelines and individual underwriting.

Lendmire’s explainer How Income Is Calculated For A Bank Statement Loan? goes deeper on the 12 versus 24 tradeoff.

Common Mistakes

• Counting transfers between your own accounts as income.
• Submitting statements with missing pages.
• Assuming the expense factor is something you pick.
• Assuming 24 months is automatically safer.
• Mixing personal and business deposits in one account.
• Ignoring a declining trend and hoping the window hides it.

The “no documentation” idea is wrong too. These files are fully underwritten, and deposits get screened line by line.

The Verdict

Use 12 months when income is rising or the older year was weak. If income is falling, expect scrutiny under both. And if the goal is a rental purchase, check whether DSCR financing makes the question moot.

If you are self-employed and want to see how the numbers work, Lendmire can help you compare bank statement loan options based on your deposits, the property, credit profile, leverage, and your goals. 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.

About Lendmire

Lendmire (NMLS# 2371349) is a mortgage brokerage built around DSCR investor lending, with programs available in 41 markets, including Washington, D.C. DSCR lenders commonly evaluate rental-income coverage instead of personal income paperwork, a practical fit for LLC-owned and multi-property investors. Terms vary by lender, property, leverage, and program. Scotsman Guide named Lendmire a Top Mortgage Workplace in both 2025 and 2026.

References

1. CFPB ATR/QM Small Entity Compliance Guide

2. Cornell LII, 12 CFR §1026.3