Routing number 121100782 was assigned to Bank of the West for accounts based in California. Bank of the West was acquired by BMO (Bank of Montreal), and the transition completed in September 2023. If this number is printed on your checks or sitting in an old direct deposit form, your account has almost certainly been migrated to BMO’s systems, and you should confirm your current routing number with BMO before you use 121100782 for any new transfer.
Which Bank Owns Routing Number 121100782
The American Bankers Association issued 121100782 to Bank of the West, a California-based institution. Routing numbers are the nine-digit codes the ABA introduced in 1910 to identify financial institutions during check processing, and they still direct electronic payments today.1American Bankers Association. Routing Number Policy and Procedures The first two digits, 12, place the number in the Federal Reserve’s San Francisco district, which covers California.
A lot of online sources attribute 121100782 to Wells Fargo. That is wrong. Wells Fargo’s primary California routing number is 121000248, with a separate variation possible for accounts opened in Southern California.2Wells Fargo. Routing and Account Number Information for Your Wells Fargo Accounts The confusion is easy to understand: both banks operated widely in California, and the numbers share a district prefix. But a single wrong digit sends money to a different institution entirely, so the distinction matters.
What the BMO Acquisition Means for This Number
BMO completed its acquisition of Bank of the West in September 2023, and former Bank of the West customers were moved onto BMO accounts. Whether 121100782 still routes correctly to your account depends on how BMO handled the migration for your specific product. Some legacy routing numbers stay active after a merger while systems consolidate; others are retired and replaced with the acquiring bank’s numbers.
The only reliable way to find out is to ask BMO directly. Call the number on the back of your debit card, or sign in to online banking and check the routing number listed under your account details. Do this before you hand the number to an employer for direct deposit, to a lender for automatic payments, or to anyone sending you an ACH transfer.
How to Verify a Routing Number Before You Use It
The most reliable place to read a routing number is a personal check. The nine-digit code sits at the far left of the MICR line, the numbers printed in magnetic ink along the bottom of the check.3GovInfo. Public Law 108-100 Check Clearing for the 21st Century Act Your account number comes next, then the check number. Copy these carefully; a single wrong digit misdirects the payment.
If you don’t have paper checks, log into your bank’s online portal or mobile app. Most banks display the routing number under account details or settings. You can also call the number on the back of your debit card and ask a representative to confirm it. After a merger like the BMO acquisition, this phone check is worth the few minutes it takes, because the number printed on checks from the old bank may no longer be valid.
The Built-In Math Check
Every ABA routing number carries a checksum that catches typos. Multiply each of the nine digits by a weight from the repeating pattern 3, 7, 1, then add the products. If the total divides evenly by 10, the number is structurally valid. If it doesn’t, at least one digit is wrong. This won’t tell you which bank the number belongs to, but it catches transposition errors before a transfer leaves your account. Most banking platforms run this check automatically when you enter a routing number.
What Happens If You Use a Retired Routing Number
Sending a payment to a defunct routing number won’t cause a permanent loss, but it will cause a delay. The receiving institution returns the transaction, and the funds eventually come back to the sender. For a paycheck routed through the wrong number, that usually means several business days without the money while the return processes and the employer resubmits with the correct information.
Standard ACH transfers settle within one to two business days on a normal path.4Nacha. How ACH Payments Work A rejected and resubmitted transfer effectively doubles or triples that timeline. If you have automatic bill payments running off the old routing number, a return can also trigger late fees from the biller before you notice the failure.
Protecting Your Routing and Account Numbers
A routing number on its own is essentially public. Anyone can look up which bank a routing number belongs to. The risk starts when someone has both your routing number and your account number, because that pairing is enough to initiate fraudulent ACH withdrawals.
Paper checks are the most common exposure point, since every check you write shows both numbers on the front. Check washing, where thieves steal mail and use chemicals to erase the payee and amount while leaving the account details intact, remains a persistent problem. Writing checks with gel ink pens makes the ink harder to remove, and dropping outgoing mail at a post office rather than an unsecured mailbox cuts the theft risk.
Business accounts can add ACH debit blocks or filters, which let you approve a list of companies and dollar limits and reject anything outside that list. Personal accounts don’t usually get that level of control, so the practical defense is monitoring. Turn on transaction alerts in your bank’s app and review statements as they arrive. Under the Electronic Fund Transfer Act, reporting an unauthorized electronic withdrawal within two business days of learning about it caps your liability at $50; the exposure rises the longer you wait.5Office of the Law Revision Counsel. 15 USC 1693g Consumer Liability
One boundary worth flagging: ABA routing numbers, including 121100782, only work for domestic U.S. transactions. Anyone sending you money from another country needs your bank’s SWIFT/BIC code instead. Handing a foreign sender a nine-digit routing number will cause the transfer to fail.