How Banks Are Assigned Routing Numbers
The ABA assigns routing numbers to US financial institutions through a formal application process. Here's how banks get their routing numbers and what the digits mean.
Every ABA routing number traces back to a formal application process administered by the American Bankers Association. Understanding how banks are assigned routing numbers helps explain why the numbering system works the way it does — and what happens when banks are acquired, restructure, or close.
The ABA's Role as Routing Number Registrar
The American Bankers Association has served as the registrar for US routing numbers since the system was established in 1910. The ABA maintains the official database of routing number assignments and processes applications from new institutions, name change requests from existing institutions, and retirement requests when routing numbers are no longer needed.
The Federal Reserve separately maintains the E-Payments Routing Directory — the operational database that payment systems actually use to route transactions. The ABA's assignments feed into this Fed directory, which is the authoritative source used by our lookup tool and by all banks and payment processors.
Who Can Apply for a Routing Number?
Any US-chartered financial institution that is eligible to hold a Federal Reserve account can apply for an ABA routing number. This includes:
- Nationally chartered commercial banks (chartered by the OCC)
- State-chartered banks (chartered by state banking regulators)
- Federally chartered credit unions (chartered by the NCUA)
- State-chartered credit unions
- Federal and state savings institutions (thrifts)
- Certain brokerage firms with banking charters
The Application Process
A newly chartered institution applies to the ABA for a routing number after receiving its banking charter. The ABA verifies the institution's charter status and Federal Reserve membership before assigning a nine-digit routing number. The assignment follows the geographic structure: the first two digits are determined by the institution's Federal Reserve district, and the ABA assigns the institution identifier portion (digits 5–8) sequentially within that district.
Multiple Routing Numbers for One Institution
An existing institution can apply for additional routing numbers when it expands into new states or acquires another bank with its own routing number infrastructure. The ABA may assign new numbers or the institution may inherit numbers from the acquired bank. Browse our bank directory to see how many routing numbers major institutions have accumulated over the years.
Routing Number Retirement
When a bank closes, is acquired, or voluntarily consolidates its routing numbers, those numbers are retired by the ABA and eventually removed from the Federal Reserve directory. Retired routing numbers are not immediately reassigned — they're held in reserve to prevent confusion with payments that may still reference the old number. After a sufficient dormancy period, they may eventually be reassigned to new institutions.
Name Changes and Rebranding
When a bank changes its name through a rebrand or merger, the routing number itself doesn't change — only the associated institution name in the directory is updated. This is why you may look up an old bank name and find the routing number still listed, often cross-referenced to the new institution name. Our lookup tool reflects current directory data, so searching for either the old or new name should surface the relevant routing numbers.
Verifying an Active Routing Number
You can verify that any routing number is currently active in the Federal Reserve directory using our free lookup tool. Active routing numbers will show the institution name, state, and supported transaction types. Inactive or retired numbers will return no results. Browse routing numbers by state to see what's active in your region.