Fractional Routing Numbers: What That Fraction on Your Check Means
Some checks display a fraction in the upper right corner — this is the fractional routing number, a legacy format still used as a backup when MICR readers fail.
If you've ever looked at a check carefully, you may have noticed a fraction printed in the upper right area — something like "21-1/1210" or "67-1348/1220." This is the fractional routing number, a legacy format that predates MICR technology. It's still printed on most US checks today as a backup for situations where the MICR line can't be read.
What Is the Fractional Routing Number?
The fractional routing number was the original way bank routing information was printed on checks before magnetic ink and electronic sorting machines existed. Human sorters used the fraction — rather than the nine-digit MICR number — to identify the destination bank. The format encodes the same information as the ABA routing number, just expressed differently.
Today, fractional routing numbers are a backup measure. If a check's MICR line is damaged, unreadable, or missing, a bank employee can use the fraction to manually determine the routing information. Our routing number lookup tool uses the standard nine-digit ABA format, which is the primary format for all electronic payments.
How to Read the Fraction
The fractional routing number has two parts: a numerator (top) and a denominator (bottom), separated by a horizontal line.
The Numerator
The numerator typically contains two parts separated by a dash: a prefix and a routing number abbreviation. The prefix is a city or state code. The routing number abbreviation identifies the specific bank within that city or state. For example, in "21-1," the "21" might be a city code and "1" identifies the institution.
The Denominator
The denominator contains two numbers separated by a slash. The first number is the ABA transit number — this corresponds to the Federal Reserve district and processing center (the first four digits of the nine-digit routing number). The second number is the Federal Reserve routing symbol for the bank's geographic area.
Together, the denominator encodes most of the same information as the first four digits of the nine-digit MICR routing number.
Fractional vs Nine-Digit Routing Number
| Format | Example | Where found | Used for |
|---|---|---|---|
| Nine-digit ABA (MICR) | 021000021 | Bottom of check (MICR line) | All electronic payments, direct deposit, ACH, wire |
| Fractional | 21-1/1210 | Upper right of check | Manual backup when MICR is unreadable |
Should You Use the Fractional Number for Electronic Payments?
No. Electronic payment systems — ACH, Fedwire, mobile deposit, direct deposit forms — all use the nine-digit MICR routing number, not the fractional format. If you need to provide a routing number for any electronic payment, always use the nine-digit number from the MICR line at the bottom of the check, or look it up using our routing number tool.
The fractional routing number is purely a human-readable backup for the rare cases where a check's MICR line is damaged. For all practical purposes, you can ignore it when setting up any electronic payment. Browse our bank directory, search by state, or explore our full guides section for more on how routing numbers work in modern banking.