[Updated November 18, 2009]
There are certainly patterns in the promotional codes, and if one is willing to try the various combinations, the reward is a better discount or … a working code!
General pattern
Except the WELCOMEn series, all codes are 8 characters. There are AT LEAST four letters out of eight.
Country
Two of the 8 characters refer to the country site
- U or US or U??????S – Home of the Brave
- C or CA or C??????A – Great White North
- A or AU or A??????U – Lucky Country
- UK or U??????K – Brittania
- CP or C??????P – Buttertown
Until now, UK members have never received a promotional code.
If there is no US, CA, UK or AU on the code, then it is DEFINITELY a promotion only for Yankees. The rest of the world is out of luck.
Member status
One character (or two) refers to the member’s status
- A, AR or AL – new subscriber
- E, ER or EX – expired (returning) subscriber
- I or N – registrants yet to finish the questionnaire
A number less than 8
If the code has a number less than 8, it may refer to the amount of the discount. For example, CODE4MAY gives 3 months for $19.95 a month, and CODE2MAY gives 3 months for $14.95 a month.
Other patterns
- Another letter of the code may refer to the message source, whether from a banner, from an email or from customer service.
- There are no month patterns. For example, SEP1CODE doesn’t imply OCT1CODE next month. JAN8DEAL isn’t necessarily only for January, either.
- WELCOME1, WELCOME2, and right now up to WELCOME18, are codes for expired (returning) subscribers in US and Canada.
An example
Put together January, US, Expired members and a number less than 8 and you have

Source: Crumpled Notebook, dated 16 January 2008
I hope this helps! Will eHarmony change the patterns now that I’ve written about it? I hope not — the patterns have been going on for three years and anyone with more than one promo code at hand and with half a brain will notice them.
UPDATE, 8 January: I see that eHarmony staff have been accessing this article frequently. Readers, watch out for changes.

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