How to Decode an Apple Serial Number (Old and New Formats)

For about a decade, every Apple serial number was a tiny encoded record. Read it correctly and an iPhone, iPad or Mac would tell you where it was built, in which year and even which week it came off the line — no internet required. That made serials a favorite tool of refurbishers and careful buyers, and a headache for sellers who lied about a device’s age.

Then Apple changed the rules. Since 2021, new products get random 10-character serials that encode nothing at all. This guide shows you how to decode the older formats, how to recognize the new one, and what to do when the serial alone can’t answer your question.

Where to find the serial number

• iPhone / iPad: Settings › General › About › Serial Number.
• Mac: Apple menu › About This Mac (click More Info or System Report for full details).
• Apple Watch: Watch app on the iPhone › General › About, or Settings › General › About on the watch.
• AirPods: Settings › [AirPods name] on the paired iPhone, or under the lid of the case.
• Box and invoice: on the barcode label — but always compare with the device itself.

Apple never uses the letters O or I in serials, to avoid confusion with 0 and 1. If you think you see one, it’s a zero or a one. On a Mac, our Mac Terminal commands guide shows how to read the serial straight from the hardware.

The 12-character format (about 2010–2020)

Most Apple devices made between roughly 2010 and 2020 use 12 characters split into five parts. Take the example C02XK0ABJG5J:

Apple has never published official tables for these codes, so factory meanings come from years of collected data by repairers. The year and week encoding, however, is consistent and reliable.

Decoding the year and week

The year letter

The fourth character tells you the year — and which half of it. Each year has two letters: the first means January–June, the second July–December.

The letters repeat every ten years, so C and D can mean 2010 or 2020. Use common sense: an iPhone 12 with a “D” serial was made in late 2020, not 2010.

The week character

The fifth character counts the week within that half-year, using the sequence 1 2 3 4 5 6 7 8 9 C D F G H J K L M N P Q R T V W X Y. So 1 is week 1 of the half, C is week 10, K is week 16. For a second-half year letter, add 26 to get the week of the year.

Back to C02XK0ABJG5J: X = second half of 2018, K = week 16 of that half, so week 16 + 26 = week 42 of 2018 — mid-October 2018.

Decode a serial instantly

Skip the tables — paste any Apple serial below. The decoder runs entirely in your browser and handles the 12-character format, the older 11-character format, and recognizes random 10-character serials:

The older 11-character format (before 2010)

Devices from the 2000s, including early iPods and Macs, use 11 characters. Here the structure is simpler: characters 1–2 are the factory, character 3 is the last digit of the year (for example 8 = 2008), characters 4–5 are the week number in plain digits (01–52), characters 6–8 identify the unit and the last three characters are the model code.

The 2021 switch to random 10-character serials

Starting with products launched in 2021, Apple moved to randomized serial numbers of 10 characters, such as H7XQ4J2LMN (an illustrative example). They contain no factory, year, week or model information. Older models that stayed in production may have kept the 12-character format for a while, so you can find both on devices sold around 2021.

Why the change? Apple hasn’t explained it in detail, but the effect is clear: you can no longer tell a device’s age, origin or configuration from its serial alone. For any iPhone 13 or later, M1 iMac and later Mac, or current iPad, you’ll need an official lookup.

Red flags when a serial doesn’t add up

Decoding is most useful as a lie detector. Watch for these:

• Date before the model existed. A serial dated 2017 on a phone sold as an iPhone 12 (released 2020) means the serial — or the phone — isn’t what it claims.
• Serial in Settings differs from the box or the case. Boxes get swapped; on Macs a different serial on the bottom case can mean a replaced housing or a rebuild from mixed parts.
• Letters O or I, or the wrong length. Apple doesn’t use them, and genuine serials are 10, 11 or 12 characters. Clones often display made-up serials.
• A random 10-character serial on an older model. It may be a legitimate replacement unit from Apple, or a mismatch. An official lookup settles it.
• The build date looks new, but the wear doesn’t. The serial shows when the unit was built, not when it was first sold or used. Check the purchase date for the real first sale.

What the serial can’t tell you — and how to find out

Even a perfectly decoded serial says nothing about locks, ownership or history. Before buying a used Apple device, look up:

• Model, color, storage and Find My status: the Model + Color + Storage + FMI check or the All-in-one Basic Info report.
• Warranty and purchase date: the iPhone warranty check shows coverage and confirms a “still under warranty” claim.
• Exact part number (MPN) and region: the part number / MPN check.
• Full history: the Apple full GSX report adds sold-by, case history and replacement records.

Use our serial number check to run them in one place, and read how to spot a fake or refurbished iPhone for the physical checks.