Apple serial number decoder: how to read a Mac serial and its manufacture date#

C02XG...JG5J decodes to a 15-inch MacBook Pro assembled at Quanta's plant in China in late September 2018. H7KX4N2P9Q decodes to nothing at all. Both are real Mac serial number formats, and the difference between them decides whether a serial can be read character by character or has to be looked up.

This guide covers every format Apple has used on Macs: how to tell which one you are holding, how to decode the 12-character format position by position, how to read a manufacture date out of a serial, the older 11-character format, and what is and isn't recoverable from the randomized serials Apple has issued since 2021. For where to find a Mac's serial and how to look it up, see the Apple serial number check guide. To skip the decoding entirely, the Macfax serial lookup returns the model and year for a serial in any format.

Which format do you have?#

Count the characters.

Apple's internal memo on the 2021 change allowed randomized serials of 8 to 14 characters; Macs have shipped with 10.

All three formats use digits and capital letters, and none uses the letters O or I. Apple says so directly in its guide to finding a serial: its numbers "use the numbers 0 (zero) and 1 (one) instead of the letters 'O' or 'I'." What looks like an O is a zero.

One trap before you start: a barcode scan of an Apple box often adds a leading S. It is a barcode marker, not part of the serial, and with it a 10-character serial looks like an 11-character one from the old format. Drop it.

Decoding a 12-character serial: a worked example#

Every Mac sold from 2010 to early 2021 carries a 12-character serial in the shape PPPYWSSSCCCC:

Apple has never published the tables behind these positions. Everything below is community-derived from years of reverse engineering, collected in the MacRumors WikiPost on decoding Apple serials and in acidanthera's open-source macserial tool. The tables are reliable for the common codes and occasionally disagree at the edges.

Positions 1 to 3: the factory#

The first characters name where the Mac was assembled. Positions 1 and 2 identify the facility, and position 3 narrows to a plant or line within it. C02 is Quanta's Tech Com subsidiary in China. A selection of codes that appear on 12-character serials:

The factory rarely matters to a buyer. It matters for diagnosing batch defects: a failure that clusters around one factory code points to an assembly-line problem rather than a design flaw.

Position 4: the year and half-year#

One letter carries both the year and which half of it the Mac was built in. X is the second half of 2018.

The cycle is 20 letters long, so it repeats every ten years: C can mean 2010 or 2020. In practice the hardware settles it. A MacBook Air with USB-C ports and a 2020 chip is not a 2010 Mac, and the configuration code in positions 9 to 12 pins the model and its release year on its own. The only case where the year letter alone cannot decide is a serial read from a photo of a device you cannot otherwise identify. Since Apple stopped issuing this format in early 2021, D (2020 H2) and F (2021 H1) are the last letters in common circulation.

The gaps are deliberate. A, E, I, O and U never appear, which keeps the alphabet from spelling words and keeps O and I from being confused with 0 and 1. B is skipped too, by convention.

Position 5: the production week#

The fifth character is the week, counted within the half-year that position 4 names. Digits cover weeks 1 to 9, and letters cover 10 to 26:

The rule that catches people out: when position 4 is a second-half letter (D, G, J, L, N, Q, S, V, X, Z), add 26 to get the calendar week. When it is a first-half letter (C, F, H, K, M, P, R, T, W, Y), the week stands as it is.

X is a second-half letter, so the G in our example is week 13 + 26 = week 39 of 2018, which ran from Monday, September 24 to Sunday, September 30. Plenty of tools report "week 13" and leave the reader to assume an early-spring Mac.

Positions 6 to 8: the unit identifier#

Three characters whose only job is to keep two identical Macs from the same line in the same week from sharing a serial. They carry no meaning. Positions 1 to 5 narrow the serial to a batch, 6 to 8 single out the unit, and 9 to 12 widen back out to the configuration.

Positions 9 to 12: the configuration code#

The last four characters point into Apple's table of configurations: model, color, storage and the other options a SKU fixes. JG5J is a MacBook Pro (15-inch, 2018) configuration. Two different codes can belong to the same marketing model when only the color or the storage differs, and there is no formula that turns a code into a model by inspection: it has to be matched against a table.

The practical route from code to model is a lookup of the whole serial, which returns the marketing name; Apple's MacBook Pro identification page then lists the Model Identifiers behind it (MacBookPro15,1 or MacBookPro15,3 for this one, depending on the graphics option). The same idea of a configuration code survives on every Mac, new or old, inside the order number on the box. The Mac model number lookup guide shows how to read it there.

Putting it together#

C02XG...JG5J is a 15-inch MacBook Pro assembled at Quanta's China plant in the last week of September 2018. Every piece of that came out of the serial itself.

Reading a Mac's manufacture date from its serial#

The manufacture date is the part of a serial people want most, and it lives in different places in each format.

On a 12-character serial, positions 4 and 5 give the week, as above. Convert the week number to a date range with any ISO week calendar.

On an 11-character serial, position 3 is a single year digit and positions 4 and 5 are the week as two plain digits. A 4 followed by 37 is week 37 of 2004.

On a 10-character serial there is no date at all. The closest proxies:

• The Boot ROM Version in System Information (Hardware). It bounds when the firmware was built, which gives a "no earlier than" date, but it is not the assembly date: a Mac assembled in June can ship with firmware from January.
• The purchase date on Apple's Check Coverage, which is usually the activation date rather than the day of sale.
• The original receipt, the device list in your Apple Account at account.apple.com, or Apple Support with the serial in hand.

A model year is a different question from a manufacture date. A serial lookup returns the model year where Apple's model name carries one, which is often all a buyer needs.

Decoding an 11-character serial#

Macs from before 2010 carry 11 characters. If you are working with a PowerBook G4, an iMac G5, an iBook or an early MacBook, this is the format on the case.

Four things differ from the 12-character format. The factory code is two characters. The year is a single digit. The week is two plain digits, which makes it easier to read than its successor's letter alphabet. The configuration code is three characters, a smaller space Apple outgrew.

The year digit is the gotcha. Because it is one digit, it repeats every ten years: a 3 means 2003, not 2013, since the format was gone by 2013. Tools built around the 12-character format often read position 3 as part of the factory code and return nonsense. If you cannot tell the model from the hardware, pair the year with the configuration code before trusting it.

The factory codes are different, too. On this format F is Fountain, Colorado, not Foxconn, and FC is Fremont, California. CK is Cork, Ireland, RN is Mexico, and XA, XB and QP are other U.S. sites. A U.S. or Irish factory code is the clearest sign you are holding a pre-2010 Mac, since most assembly had moved to East Asia by the time the 12-character format took over.

Apple's Check Coverage sometimes refuses an 11-character serial because the coverage record has aged out. That does not mean the serial is invalid.

The F prefix is not a refurbished flag#

A persistent myth in the used market says a serial starting with F marks a refurbished Mac. It does not. On a 12-character serial, F, F1, F2, F7, FC and FK are Foxconn factory codes, and millions of new Macs carry them. On an 11-character serial, F is Fountain, Colorado. On a randomized serial the first letter means nothing.

Refurbished status lives in the order number on the box, not in the serial. An order number starting with F, as in FNEH3LL/A, is an Apple Certified Refurbished unit; M is new retail and N a service replacement. The Mac model number lookup guide covers the prefixes and their limits on Macs.

Serials from 2021 on: what you can and can't decode#

In March 2021, internal AppleCare communications reported by MacRumors, and confirmed the same day by AppleInsider and 9to5Mac, said Apple was moving to randomized serials that "will no longer include manufacturing information or a configuration code." The widely understood reasons were privacy (structured serials let outsiders estimate production volumes) and counterfeiting (anyone with the tables could generate a plausible serial).

The rollout went model by model rather than on one date. The 14-inch and 16-inch MacBook Pro with M1 Pro and M1 Max, from October 2021, were among the first Macs with randomized serials. The 24-inch iMac with M1, launched earlier in 2021, still shipped with 12-character serials. Every M2, M3 and M4 Mac carries a randomized one. So "a 2021 Mac" does not settle the format: count the characters.

What no longer works. Anything that reads the characters. Factory tables, year letters, week alphabets and configuration codes have nothing to work on, and a decoder that returns a factory or a date for a 10-character serial is guessing.

What still works. The serial still belongs to exactly one Mac and one configuration; the characters simply don't say which. It has to be looked up rather than decoded. The Macfax serial lookup returns the model, device class and year for a randomized serial the same way it does for an older one, and Check Coverage returns Apple's marketing name and warranty status. With a list rather than one serial, the bulk lookup identifies the whole inventory in one run.

What didn't change. Every other identifier on the Mac kept its structure in 2021, and each still carries information offline:

On a recent Mac, the order number is the richest offline source, and on a custom-configured one the Z-style part number says more about the build than anything else on the machine. The Mac model number lookup guide reads each of them.

"Invalid serial" on a randomized Mac. A randomly typed 10-character string almost never matches a real serial, so a refusal is usually a typo: an O for a 0, an I for a 1, or a leading S from a box barcode. After that, in rough order: a brand-new Mac not yet in Apple's records (allow a day or two), a flagged record, a regional restriction on Check Coverage, or a short lag after a logic-board repair.

The serial after a logic-board swap#

When Apple or an Apple Authorized Service Provider replaces a Mac's logic board, the new board arrives blank. The technician writes the Mac's original serial onto it with Apple's internal service tooling (the Blank Board Serializer, now part of Apple Service Toolkit 2, reached through GSX). Done right, nothing changes from the owner's side: About This Mac, Apple's warranty records and Check Coverage all show the same serial as before.

Done wrong, a repair leaves one of three traces:

• A blank serial. About This Mac shows no serial, or zeros. The step was skipped or interrupted. This is the common case and the fixable one: the same provider can usually write the serial, because the tool accepts a write only when no serial is present.
• A mis-flashed serial. The board carries a serial, but the wrong one, sometimes a test value or another unit's number. Because a serial is already present, the standard tool refuses to overwrite it, and fixing it means a slow escalation inside Apple.
• A mismatch with the case. The board reports one serial and the etching on the case shows another. This is the variant that surfaces months later when a buyer cross-checks.

No shop outside Apple's authorized network can write a Mac serial. Anyone offering to is using credentials that will not last, or is not doing it at all.

The board's own serial is a different number. The main logic board also carries a printed serial of 13 or 17 characters identifying the board as a part. It is not the serial system_profiler reports or Check Coverage recognizes, and the two disagreeing is normal.

The check before buying. Run system_profiler SPHardwareDataType (or open About This Mac) and compare the serial with the one etched on the case. They should match exactly. Then look up both: the model returned should match the chassis in front of you. A mismatch is not automatically a deal-breaker, since warranty board swaps are legitimate and common, but the seller should be able to explain it, ideally with the repair's work order.

Common misreads#

Etched serials are small and light gray, and the same few characters cause most of the trouble: 8 and B, 0 and D or Q, 1 and 7, 5 and S. Remember that a serial never contains O or I. On a Mac that starts up, System Information's File → Speak Serial Number (⌘-4) reads the true value aloud while you check the case; the serial number check guide lists every other place to read it.

What this means#

An 11- or 12-character serial is a small record of where and when a Mac was built: the factory, the half-year, the week and the configuration, all readable with the tables above. A 10-character serial is a reference number and nothing more, and the only way from it to a model is a lookup. The Macfax serial lookup handles both, and the family pages for MacBook Pro, MacBook Air, iMac, Mac mini, Mac Studio and Mac Pro list every model with its identifiers.