The routing number guide

What a routing number is

A routing number— formally the ABA routing transit number (RTN) — is a 9-digit code that identifies the financial institution responsible for a payment. The American Bankers Association created the system in 1910, and it’s still how checks, direct deposits, and transfers find the right bank. Think of it as the bank’s mailing address within the US payment network: your account number says which account, the routing number says which bank.

The ABA format, digit by digit

Every routing number is exactly nine digits, and each part means something:

• 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 single digit calculated from the first eight to catch typos.

How the checksum works

The ninth digit isn’t arbitrary — it’s a checksum. Label the digits d1 d2 d3 d4 d5 d6 d7 d8 d9. A valid routing number satisfies this weighted formula, where the total must be a multiple of 10:

3·(d1+d4+d7) + 7·(d2+d5+d8) + 1·(d3+d6+d9) ≡ 0 (mod 10)

The repeating 3, 7, 1weights let the formula catch the most common data-entry mistakes — a single mistyped digit, or two adjacent digits swapped. If the weighted sum isn’t divisible by 10, the number is invalid and a bank’s system will reject it before any money moves.

How to find your routing number

• On a check: it’s the left-most 9-digit number printed in the special MICR font along the bottom edge, before your account number and the check number.
• In online or mobile banking: open your account details; most banks display the routing number there directly.
• On your bank’s website: banks publish their routing numbers, often broken out by state and by transfer type.
• On a statement: many monthly statements list the routing number in the account-summary section.

If you bank with an online-only institution and don’t have paper checks, the in-app account details or the bank’s help center are the most reliable source.

ACH vs. wire routing numbers

Many banks use more than one routing number, and using the wrong one can delay or misroute a payment:

• ACH routing number: for Automated Clearing House transfers — direct deposit of your paycheck, bill payments, and most app-to-app transfers. ACH moves in batches and is typically free.
• Wire routing number: for domestic wire transfers, which settle the same day and usually carry a fee. Some banks use a different routing number for wires than for ACH.
• International transfers: these usually rely on a SWIFT/BIC code rather than an ABA routing number. Ask your bank for the right details.

When a form or a person asks for your routing number, confirm whether they need the ACH or the wire number, then use exactly what your bank lists for that purpose.

Safety tips

• The number itself is public. Your routing number is printed on every check you write, so on its own it isn’t a secret and can’t drain your account.
• The risk is the pair. A routing number plus your account number can be used to set up ACH debits. Share both only with employers, billers, or people you trust.
• Verify before you send. Before a wire or large transfer, confirm the recipient’s routing and account numbers through a channel you initiated — fraudsters often send fake “updated” banking details by email.
• Watch for spoofed sites. Look up routing numbers on your bank’s official site or app, not from a search-ad link, and never enter them on a page you reached from an unexpected message.
• You can verify the format. A legitimate routing number is always 9 digits and passes the 3-7-1 checksum above; anything else is a typo or a fake.

Routing numbers tell you where your money lives. To understand how safe it is once it’s there, see how FDIC insurance protects your deposits, try the FDIC insurance calculator, or scan your bank for its health signal.