Winter begins at different times depending on the definition used:

• Astronomical winter starts at the winter solstice, which usually falls on December 21 or 22 in the Northern Hemisphere. For 2025, it will begin on Sunday, December 21, and end on Friday, March 20, 2026. This is based on Earth’s tilt and orbit around the Sun, marking the shortest day of the year.

• Meteorological winter, used for weather statistics and forecasting, starts earlier, on December 1, and lasts through February 28 (or 29 in a leap year). For 2025-2026, meteorological winter runs from December 1, 2025, to February 28, 2026.

Thus, winter can be said to begin either on December 1 (meteorological) or around December 21 (astronomical), depending on context and location in the Northern Hemisphere.