What is a date code
A date code is a short marking a manufacturer prints on a component to record when it was produced. It is one of the fastest ways to gauge the age of a part, which matters when you are buying from the secondary market and want to confirm the stock is as new as the seller claims. For a fuller definition, see the date code glossary entry.
Common date code formats
There is no single universal standard. These are the formats you will meet most often.
| Format | Meaning | Example | Decodes to |
|---|---|---|---|
| YYWW | 2-digit year, 2-digit week | 0530 | Week 30 of 2005 |
| WWYY | 2-digit week, 2-digit year | 3005 | Week 30 of 2005 |
| YYYYWW | 4-digit year, 2-digit week | 202430 | Week 30 of 2024 |
| YYMMDD | 2-digit year, month, day | 210615 | June 15, 2021 |
How to read a YYWW code
YYWW is the most common format. Take the code 2148. The first two digits, 21, are the year: 2021. The last two, 48, are the week: week 48, which falls in late November. So the part was made around late November 2021. Because the year is only two digits, the century is assumed to be the 2000s unless that would place the date in the future, in which case the 1900s reading is used instead.
Date codes and counterfeit detection
A date code cannot prove authenticity, but an impossible one is a genuine warning sign. This tool flags two things that should never appear on a legitimate part:
- Invalid week number. A week of 00 or greater than 53 does not exist. A re-marked part often carries a nonsense week.
- Date in the future. A manufacture date that has not happened yet is impossible and points to a fabricated marking.
Treat these as one input among many. For the full picture, read our guide to preventing counterfeit components, and buy through authorized or vetted sources.
Date codes vs lot codes
A date code records when a part was made. A lot code identifies the internal manufacturing batch and is generally not decodable to a date without the manufacturer's own records. If a marking will not decode as a date here, it may well be a lot code. This tool decodes date codes only.
Frequently asked questions
What is a date code?
A date code is a marking a manufacturer stamps on a component to record when it was made. The most common form is YYWW, a 2-digit year followed by a 2-digit week of the year. It tells you the age of the part, which matters when buying on the secondary market.
What does YYWW mean?
YYWW is a 2-digit year followed by a 2-digit week number. For example, 0530 means week 30 of 2005, around late July 2005. Some manufacturers reverse the order (WWYY), so always check both readings.
Can a date code prove a part is counterfeit?
On its own, no. But an impossible date code is a strong warning sign. A week number above 53, or a manufacture date in the future, cannot be legitimate and points to a re-marked or counterfeit part. Treat it as one signal among many and verify through an authorized source.
Can you decode a lot code?
No. A lot code is an internal manufacturing batch identifier and is generally not decodable to a date without the records held by the manufacturer. This tool decodes date codes only. If a marking will not decode as a date, it may be a lot code.
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