- What is a routing number?
- A routing number (also called an ABA routing transit number or RTN) is a 9-digit code that identifies a US financial institution. Created by the American Bankers Association in 1910, routing numbers are used for processing checks, wire transfers, direct deposits, and ACH payments. There are approximately 28,000 active routing numbers in the United States, managed through the Federal Reserve’s FedACH directory. For international transfers, you may need an IBAN instead. UK banks use sort codes for domestic payments.
- How is a routing number validated?
- Routing numbers use a weighted checksum algorithm called the ABA 3-7-1 method. The formula is: 3(d1) + 7(d2) + 1(d3) + 3(d4) + 7(d5) + 1(d6) + 3(d7) + 7(d8) + 1(d9). If the sum is evenly divisible by 10, the routing number is valid. For example, for routing number 021000021: (3×0) + (7×2) + (1×1) + (3×0) + (7×0) + (1×0) + (3×0) + (7×2) + (1×1) = 30, which is divisible by 10.
- Where can I find my routing number?
- Your routing number appears at the bottom-left of your checks as the first 9 digits (before the account number). You can also find it in your bank’s online banking portal, on your bank statements, or by contacting your bank directly. Note that a single bank may have multiple routing numbers for different regions, wire transfers vs. ACH, or paper vs. electronic transactions. For example, JPMorgan Chase uses 021000021 in New York but different numbers in other states.
- What do the digits in a routing number mean?
- The 9 digits encode specific information: digits 1–2 indicate the Federal Reserve district (01=Boston, 02=New York, 03=Philadelphia, 04=Cleveland, 05=Richmond, 06=Atlanta, 07=Chicago, 08=St. Louis, 09=Minneapolis, 10=Kansas City, 11=Dallas, 12=San Francisco). Digits 3–4 identify the Federal Reserve branch or special processing center. Digits 5–8 identify the specific financial institution. Digit 9 is the check digit calculated using the 3-7-1 weighted algorithm.