If you look up how to say “happy new year” in Japanese on Google, you will find “あけまして おめでとうございます”, and probably because of that, some of my students say this to me now. But actually this phrase is only used after the new year has started. The word “あけまして” comes from “明ける” which means “to begin”. So “あけましておめでとうございます” can be used after midnight on New Year’s Eve, but before that time, you should use “よい おとしを”, which means “have a happy new year!”
