What is a routing number?

The 9-digit ABA number, in plain terms

A routing number — formally an ABA routing transit number (RTN) — is a nine-digit code created by the American Bankers Association in 1910 to speed up check processing. Every federally chartered and state-chartered bank that handles routed transactions has at least one. When money moves between banks, the routing number is how the network knows where to send it.

Think of it as a postal address for a financial institution. Your account number is the apartment number inside that building. A transfer needs both: the routing number to reach the right bank, and the account number to reach the right account.

How the nine digits are structured

The digits are not random. The structure is fixed and even self-checking:

• Digits 1–4 (Federal Reserve routing symbol): identify the Federal Reserve district and processing center that handles the bank.
• Digits 5–8 (ABA institution identifier): identify the specific bank.
• Digit 9 (check digit): a checksum calculated from the first eight digits. It lets software catch most typos before a payment is even submitted.

The check-digit math (for the curious)

The checksum uses a weighted sum: multiply the digits by 3, 7, 1, 3, 7, 1, 3, 7, 1 in order, add the results, and a valid routing number’s total is evenly divisible by 10. This is why a single mistyped digit almost always produces an invalid number rather than silently routing money to the wrong bank.

Where to find your routing number

• On a check: the first group of nine digits along the bottom, printed in the special MICR font, between the two colon-like symbols. The account number follows it.
• In your banking app or online banking:usually under account details or “account & routing number.”
• On your bank’s website or by phone: banks publish routing numbers openly because they are not confidential.

If you do not have checks, the app or website is the most reliable source. Avoid third-party lookup sites for anything you will actually send money with — confirm the number directly with your bank.

Why your bank may have more than one

Large banks often hold several routing numbers, and the right one can depend on three things:

• The state where you opened the account.Many national banks assign routing numbers by region, so your number can differ from a friend’s at the same bank.
• The type of transaction. Some institutions use one routing number for ACH (direct deposit, bill pay) and a different one for domestic wire transfers.
• Mergers. When banks combine, legacy routing numbers can linger for a transition period.

For paychecks and bill payments you almost always want the ACH routing number. For a wire, ask specifically for the wire routing number — using the wrong one is a common cause of delayed or returned wires.

Routing numbers and your money’s safety

A routing number is public, so knowing it alone does not let someone drain your account. The risk comes when a routing number is paired with your account number, which together can authorize ACH debits. Treat the pair like a password: share it only with payers and billers you trust.

Separately, the routing number has nothing to do with whether your deposits are insured. That protection comes from the FDIC (for banks) or the NCUA (for credit unions), up to $250,000 per depositor, per insured institution, per ownership category. Learn how that coverage works in our bank safety guide, and see the difference between the two insurers in FDIC vs NCUA.

Common mistakes to avoid

• Using a deposit slip routing number for an outgoing wire — deposit slips sometimes show an internal number, not the one for transfers.
• Assuming an online bank’s routing number matches the partner bank that holds the deposits — check the app, not a search engine.
• Reusing an old routing number after a bank merger without confirming it still works.

When in doubt, send yourself a small test transfer first, or confirm the number with your bank before a large or time-sensitive payment.