The first day of winter depends on which definition is used and which hemisphere you are in.

Northern Hemisphere

  • Astronomical winter (what most people mean by “first day of winter”) starts on the winter solstice, around December 21 each year.
  • Meteorological winter (used by many weather agencies) starts on December 1 and runs through the end of February.

So when people ask “when is first day of winter” in current news and forum discussions, they are usually talking about the winter solstice date, which in 2025 falls on Sunday, December 21 in the Northern Hemisphere.

Southern Hemisphere

  • The seasons are flipped: the first day of winter (astronomical) is around June 20–21, on the June solstice.
  • Meteorological winter there runs from June 1 to August 31.

Why people argue about it

  • Some online forum threads joke about how “both are right” or forget the Southern Hemisphere entirely, because many people only think about December in the North.
  • Media, weather sites, and almanacs increasingly spell out both dates (Dec 1 vs. Dec 21) to avoid confusion and to match how people talk about “winter starting” in day‑to‑day life.

In short: if you mean the solstice, the first day of winter is around December 21 in the Northern Hemisphere and June 20–21 in the Southern Hemisphere; if you mean the weather‑season, it’s December 1 or June 1 respectively.

Information gathered from public forums or data available on the internet and portrayed here.