As in 'This food is not expired' or 'I recently renewed my membership so it is not expired'. A word I could use in place of 'not expired' in both these sentences (so not words like 'edible' or 'valid' which are too specific).
3Not a single word, but "still good" would work where I'm from. "This food is still good" and "I recently renewed my membership so it is still good" both make sense to me– elmer007May 19, 2016 at 19:37
Why is "valid" too specific? Your membership is valid until it expires. If you are asking for antonyms of "expire" in general, you should check a dictionary first add what you found (or didn't find).– user3169May 19, 2016 at 19:50
4How about "in date", or simply "unexpired"?– JavaLatteMay 19, 2016 at 19:58
@elmer007 still good works, though I realise now I'm looking for something more formal– James HiewMay 19, 2016 at 20:13
1For membership, passport or driving licence you can also use "current".– JavaLatteMay 19, 2016 at 20:20
The opposite is simply unexpired. Not used very frequently, but it is a real word.
More common usages are either more specific (e.g. fresh as opposed to expired when talking about food spoiling), or use more words (e.g. still good, which is probably used more often than unexpired to mean the same, but is rather informal).
How about active?
Though I would consider using inactive as the opposite in this case.
P.S. Last time I used effective as the opposite of expired for a price object (in programming)
As for passports, identification cards, licenses, etc, the word that comes to my mind is "issued". Then again, if something isn't "expired" it must be "valid".