How to I prove my legal age so that I can drink in New Zealand?

You can definitely use your passport to prove your age. It's used by visitors all the time here in NZ, so it won't be unusual, and your bartender will certainly have seen a passport before.

There are 3 forms of accepted ID. An NZ drivers license, any current passport and a HANZ18+ card. You can find a form for an 18+ card here:

https://www.alcohol.org.nz/alcohol-management-laws/nz-alcohol-laws/age-the-law/approved-id

It costs $50 but could be a good idea if you're planning on being out often because taking your passport around with you while drinking could result in a lost passport.

Supermarkets are typically very strict with these rules, but bars and clubs might be more lenient.

I live in NZ.

Although I don't drink, I have used US-issued ID documents in New Zealand for other purposes. Based on my experience, a passport is always fine as ID, whereas an ID card (especially one that isn't a driver's license) is sometimes trickier. I've also purchased alcohol for cooking purposes, although I don't recall which ID I used (which probably means I used a state ID successfully, rather than a passport).

With my state ID card, I did encounter two difficulties:

• In some cases, mostly when forms were involved, the difference between "driver's license" and "state ID" mattered a LOT. A driver's license is "foreign driver's license", so easy to put on forms; a state ID isn't a "foreign driver's license", and it isn't a "national ID", so it ended up being rejected (or required a manager to come over and assist).
• The American-style "month/day/year" birthdate ordering, used on ID cards but not passports, is unfamiliar to New Zealanders. If that would make the difference between "I'm 18!" and "I'm, uh, still 17", this might be a problem for you.

With a passport, on the other hand, nobody has ever complained or had difficulty with it (although it IS a bit bulky in one's pocket).

If you want to definitely have your ID accepted, therefore, I'd suggest the passport. If you're okay with possibly being turned away, you might be able to try with the ID card.

Not a New Zealander but, as a seasoned traveller, yes you want to use your passport.

I have on occasion completely forgotten that my UK driving licence only may be accepted on such occasions, particularly when in the US. With my passport safely stowed in my hotel room's safe, I've found myself relying on the licence that lives in my wallet, with only mixed success. When I'm refused service I appreciate why that is and chastise myself for forgetting to bring my passport out with me once again. When travelling, I always assume this experience will be the same or similar, no matter what country I'm visiting.

To be fair, if you're just grabbing an unplanned quick pint during a day otherwise filled with sightseeing, you may not want to take your passport out with you, in which case you'll have to make do with orange juice. :)

Sorry it's been pointed out to me that I'm not up to date; they changed to a permitted list with the new governing act in 2012, use your passport.

While Luke is correct that the three most valid forms of ID here in NZ are NZ Drivers License, a Passport (current or in some cases recently expired), and the HANZ18+ Card. The minimum legal requirements for age ID can however be covered by other documents and are as follows:

• ID needs a photo that is recognisably the subject.

and

• a serial number that can be checked against an issuer's database.

and

• the subject's date of birth.

Your State ID may fulfill these requirements or not, there are a number of high schools whose student IDs meet those requirements and I had classmates who used their school IDs to purchase alcohol senior year.

However all of that is moot if the barkeeper or bouncer decides they don't want to serve you, because they don't trust the ID you have presented or for any other reason at all. I'd strongly suggest sticking with the passport as it should minimise cause for confusion or argument, and always be polite to the bar staff.

I've travelled to New Zealand (8 years ago) and used my UK drivers license as ID for purchasing alcohol (and in the 3 weeks I was there I only got asked the once). But as others have said Passport will also always be accepted as proof of age ID.