I have done some searching, most I see were asking about cabin carry on...

I am planning to fly AKL-ZQN. But I have not pack yet and not sure how much my luggage would weight. I have read it cost an arm & leg if priced at airport (something like 15NZD per Kilo?!)

So say, if I purchased 20kg allowance when I book the ticket online, but ended up it is over, how's the calculation works? Say if it is 1-2kg over?

I have never fly JQ before. And with my *G, luggage weight is never a concern for me.