How to read a serial number

Every US banknote serial carries four separate pieces of information, and most tools throw three of them away by accepting digits only. Here is what each part means, and a decoder that reads all of it.

Denomination $1$2$5$10$20$50$100

Serial number

Decode this serial Decode

This reads the note rather than pricing it: which Federal Reserve bank issued it, which series it belongs to, which block it came from, and whether it is a replacement.

Try B12345678A MB12345678C PF00123456*

The anatomy of a serial number

Take MB12345678C from a $20 note. It breaks into four parts, read left to right:

• M — series letter. Series 2013. Only $5 and above carry one.
• B — district letter. The Federal Reserve Bank of New York, district 2.
• 12345678 — the number of this note within its block.
• C — block suffix. The third suffix in sequence for that series and district, so two earlier blocks were filled before this one. A star here instead means the note is a replacement.

On a $1 the same serial would have only one prefix letter, because $1 and $2 notes have never carried a series letter. That is the single most useful rule for reading a serial: count the letters before the digits. One means a $1 or $2 — or a $5 and above from Series 1995 or earlier, before the two-letter format arrived with Series 1996. The $2 serial number page covers the one-letter case in detail, since it is where most of the confusion lands.

The twelve districts

The district letter tells you which Federal Reserve Bank put the note into circulation. All twelve print in the hundreds of millions, so a district is not scarcity — it is provenance.

The series letters, which are not in order

On a $5 and above, the first letter encodes the series. Reading it as an alphabet is the mistake almost every serial guide makes: the letters were assigned as printing began for each denomination, not by date, so they do not sort chronologically and two letters can map to the same year.

Blocks, and why the numbers stop early

A block is one combination of prefix and suffix letters — every note sharing that combination belongs to the same block. When a block is exhausted the suffix advances to the next letter, and the numbering starts over.

A block does not run all the way to 99,999,999. Skip numbering means the presses leave gaps, and the real ceilings are 96,000,000 on $1 through $20 and 99,200,000 on $50 and $100. This matters more than it sounds: it means a solid 99999999 on a modern note is not rare, it is impossible, and a note offered with one is either from an uncut collector sheet or is not what it claims.

Letters that never appear

O is never used, because it is indistinguishable from a zero at serial-number size. Z is reserved for test printings that do not enter circulation. Neither letter appears in a district position, a series position or a block suffix on a circulating note.

The star

When a sheet is spoiled during printing, the Bureau of Engraving and Printing cannot reprint it with the same numbers — serials are never repeated. It prints a replacement from a separate run, whose serials end in a star instead of a suffix letter. How much that matters depends entirely on how big the replacement run was, which the star note lookup answers.

The small FW, which is not part of the serial

US currency is printed at two facilities. Notes from the Fort Worth, Texas plant carry a small FW next to the front plate number; notes without it were printed in Washington, DC. It sits apart from the serial number and does not change the district — a Fort Worth note can be issued by any of the twelve banks.

Questions

What do the letters on a dollar bill mean?

On a $1 or $2, the single letter before the serial digits is the Federal Reserve district that issued the note, A for Boston through L for San Francisco. On a $5 and above the first of the two letters is the series and the second is the district. The letter after the digits is the block suffix, or a star if the note is a replacement.

What does the letter at the end of a serial number mean?

It identifies the block. A block is one combination of prefix and suffix letters, and it runs until its numbers are used up — at which point the suffix advances to the next letter. O and Z are skipped, so a block suffix runs A, B, C and so on through Y, excluding O.

Why do serial numbers stop at 96,000,000?

Because of skip numbering. The presses do not print every number in a block: on $1 through $20 a block effectively tops out at 96,000,000, and on $50 and $100 at 99,200,000. A note numbered above the ceiling for its denomination did not come from ordinary circulation printing.

Which letters are never used in a serial number?

O and Z. O is too easily confused with zero, and Z is reserved for test printings that do not enter circulation. If you read an O or a Z on a note, look again — it is almost always a zero or a 2.

How do I find the series year on a bill?

It is printed on the face of the note, near the portrait, as "SERIES 2017" or similar. On a $5 and above you can also read it from the first letter of the serial, though the letters are not in alphabetical order by year.