The Ordinary Batch Codes: Year Digit + Month Letter

Deciem's newer codes encode a year and a month letter — and its older four-character codes cannot be decoded by anyone. Here's how to tell them apart.

4 min read · Updated July 2026

Anatomy of the code `4A01`

Characters	What they encode
`4`	Last digit of the production year — 2024
`A`	Month letter: A = January … L = December
`01`	Production line — no date information

Worked examples

Decoded live by the same engine that powers the checker — not transcribed by hand.

4A01January 1, 2024medium confidence

January 2024.

5F02June 1, 2025medium confidence

F is the 6th letter — June.

Two generations of code

Deciem's newer batch codes start with a year digit, then a month letter running A for January through L for December, then a line number. 4A01 is January 2024.

The older four-character codes — TGD1, 1dg1 and similar — use an internal system Deciem has never published. They are not decodable, by us or by anyone else, and any site claiming to decode them is inventing the answer. On those products, use the printed best-before date.

Reading one by hand

First character a digit and second a letter A–L? Newer format. The digit is the year, the letter is the month.
Anything else — letters first, mixed case, no leading digit — is the old format. Don't try to decode it.

Why we stop at the month

The trailing digits are ambiguous: some sources read them as a day of the month, others as a production line. We decode to the month rather than pick one and present a guessed day as fact. An unopened Ordinary serum has roughly a three-year shelf life, so a fortnight of imprecision changes nothing that matters.

FAQ

Does vitamin C from The Ordinary really go off faster?

Pure L-ascorbic acid oxidises — that is what the yellow-to-brown colour shift tells you. Once it has turned, potency is gone regardless of what the batch code says.

Brands that use this code (2)

The format belongs to the manufacturer, not the label on the bottle — every brand below is stamped by the same plants and reads the same way.

Other code formats

Not sure which code on the pack is the batch code? How to Find Your Batch Code