The numbers game

Unpacking the bank account, routing, debit, credit and other numbers that ultimately control how we send and receive money

U.S. banks have debit card numbers, credit card numbers, bank account numbers, and routing numbers to control how we send and receive money. SWIFT codes also come into play for international wire transfers. And even though these numbers are linked to the same account holder, the numbers themselves are discrete.

This number soup is ultimately a good thing. After all, too much overlap would exacerbate the risk of fraud. The numbers serve as codes that identify where your money comes from and where it needs to go. And the codes have built-in protection measures to guard against fraud.

Let’s look at the numbers, where they come from, and how, exactly, they’re useful.

Routing number

The routing number is one of two numbers associated with a bank account and an important element of checks and ACH payments. As the name suggests, this number routes money to the bank by providing a series of identifiers that pinpoint exactly where the account resides.

Specifically, a routing number contains 9 digits.

These first four numbers together are called the Federal Reserve Processing Symbol. The first two digits are generally 01-12 and refer to the head branch of the Federal Reserve district that serves the bank. The districts start with 01 in Boston and end with 12 in San Francisco, often encompassing surrounding states as well. A range of 61-72 is assigned to non-bank payment processors, and the number 80 to travelers’ checks.

The third digit identifies the regional Federal Reserve processing center assigned to the bank within its district. The fourth digit is used to indicate the bank’s location, or specifically, how close it is to the Federal Reserve city proper indicated by the first two digits.

The next four digits are a unique identity code assigned to the bank by the American Bankers’ Association. Each bank within a Federal Reserve district has a unique ABA code, which means that each bank in the country has a unique routing number determined by all the factors above. Customers of a particular bank in a region all use the same routing number, the one assigned to their bank; only their account numbers are unique.

The final digit of the routing number is a “check digit,” which is generated algorithmically to ensure the routing number’s validity: An arithmetic formula applied to the numbers must result in a number divisible by 10. While this can’t prevent fraud made possible by stealing a check, say, it can ensure that no numbers are transposed or mistaken when a routing number is provided or that the number isn’t completely—and sloppily—made up.

While checks are only associated with a checking account, ACH payments, such as direct deposits, can be routed directly into a savings account, but the same routing number usually applies to both kinds of accounts if they’re housed at the same bank.

Account number

A bank account number is the unique number associated with a checking or savings account at a bank. In the United States, there’s no standard format for account numbers. Each bank assigns numbers in its own way; the methodology is not publicized due to security concerns, but it almost certainly is not random. Most bank account numbers have between 8 and 12 digits—though they can range from 5 to 17. Bank account numbers are unique within each bank—or at least they’re supposed to be. In 2011, Bank of America mistakenly gave two customers the same bank account number, which led to $30,000 worth of Social Security payments getting deposited in the wrong person’s account.

Credit card number

A credit card number generally contains 16 digits. Like the routing number, the credit card number is not assigned randomly and provides quite a bit of information.

The first six digits are known as the Issuer Identification Number (IIN). The first digit is a Major Industry Identifier (MII) and shows what industry the card issuer belongs to. For example, credit cards issued by airlines have an MII of 1. The entertainment and travel industry uses 3 (which includes Diner’s Club cards and American Express). 4, 5, and 6 all indicate the financial and banking industry and are specific to specific institutions: All Visa cards begin with 4, MasterCard with 5, and Discover with 6. 7 through 9 are reserved for petroleum and healthcare industries and national standards bodies.

The next five digits identify the bank or network that issued the card, and all cards issued by the same bank and program share their IIN. For instance, an IIN of 475050 indicates a JPMorgan Chase Visa Credit Card, while an IIN of 526219 indicates a Citibank MasterCard American Airlines AAdvantage Debit Card. If the program is vast, it can have multiple IINs. For instance, Bank of America Visa Credit Cards have several possible IINs.

Digits 7-15 on the credit card provide a unique credit card account number. This number is different from any bank account numbers a consumer may have, partly because many people hold credit cards from different institutions than their banks, and partly to prevent fraud. If a credit card is lost or stolen, it can be easily canceled and the number replaced. When this happens, a new credit card is issued with a different account number at digits 7-15. However, because no bank account information was stolen, it’s never necessary to cancel any other accounts.

The final digit in the credit card number is a “check digit,” which serves a similar purpose as that in the routing number. This digit on the credit card is applied to an equation called the Luhn Formula to assess the validity of the whole credit card number. The check digit is assigned to each card to validate the formula, which requires doing some basic arithmetic (addition, multiplication, and division) several times over to ultimately achieve a remainder of 0. Incidentally, IBM scientist Hans Peter Luhn invented this formula in the 1950s, when credit cards were just being invented. He used it mainly as a check against erroneous manual data entry, and the formula has persisted as a useful anti-fraud measure. Computers do the check instantaneously and can reject a card payment immediately if the formula doesn’t hold true.

To make matters even more complicated, American Express cards only have 15 digits. That’s because while other card networks like Visa, MasterCard, and Discover rely on banks to issue their cards, American Express issues its cards itself. Therefore, no IIN is used to identify a bank within the credit card number. Rather, American Express card numbers have a different structure: a two-digit MII (which is 37 or 34), a two-digit number indicating type of card and currency used, a seven-digit account number, and a check digit.

The numbers on the back of a credit card are the last four numbers of the number on the front, and the three-digit CVV, or card verification value. (On American Express cards, this number has four digits and is found on the front). This number is an important security measure because it verifies that the cardholder has the physical card (as opposed to just the number) when making online purchases. It also makes stealing a credit card number trickier because merchants are prohibited by law from storing the CVV. So even if they store a credit card number and get hacked, a thief can’t do much with the number without the CVV.

Debit card number

A debit card number is put together the same way as a credit card number, with the MII, IIN, unique account number, and check digit that applies to the Luhn Formula. A debit card, however, is linked directly to a checking account, even though it does not include the account number. Like with a credit card, this is largely for security reasons. For example, if the card is lost or stolen, it can be easily replaced with a new number, while the checking account number stays the same. The debit card can be frozen without having to freeze the account itself, therefore having no effect on ACH or check transactions and causing much less of a headache. Similarly, debit cardholders who have a joint checking account have different debit card numbers, though the cards draw on the same account. If one cardholder loses his card, it can be replaced without compromising the other holders’ cards or the account itself.

Wire transfer routing number

A wire transfer number comes into play when accounts at American banks receive money transfers from other U.S. banks. This number is assigned to banks by the ABA, just like a normal routing number. However, while check routing numbers differ geographically, one bank may use a single wire transfer routing number for all incoming transactions. For example, all incoming wires to Bank of America accounts use the wire transfer number 026009593. All incoming wires to Wells Fargo accounts use 121000248. Further identifying information such as the account number helps direct the funds to the right person.

SWIFT codes

SWIFT is another way of directing money from one bank to another, but is used internationally and for money transfers that cross national borders. SWIFT codes often come into play when initiating wire transfers both from another country to the United States and from a U.S. bank to one in another country.

A SWIFT code is an alphanumeric string of 8 to 11 characters in a very specific format. The first four characters are letters indicating the bank code; the next two letters are the country code; the next two characters can be letters or numbers that indicate the bank’s location within the country; and the last three characters, which are optional, indicate the bank’s branch code. If the destination is the bank’s primary branch, the last three characters are omitted. For example, Bank of America’s SWIFT code for wires paid in U.S. dollars at the New York City branch is BOFAUS3N. The code only has eight digits, because the payments are sent to the primary branch. Banks’ SWIFT codes differ for payments in foreign or domestic currency.

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