How many days is it until Christmas?
The date of today is 20th of March, 2023 (in GMT) and the next Christmas is on the 25th of December, 2023, so there are 279 full days and some more time until Christmas, but the expression "days until an event" is typically meant to include the remaining time that is less than 24 hours as an additional day to avoid having to say "There are 0 days left" on the last day of the countdown, therefore I can say:
It is 280 days until Christmas.
Since I don't know which time zone you are in I cannot guarantee that the answer is accurate for your exact case. If you would like to know how many days are until Christmas in a specific timezone, let me know the timezone or the current date in that timezone.
It worth noting that there are many websites that can show you practical countdown timers until common events, especially Christmas. The benefit of those sites is that they can use the timezone of your device to show accurate results specific to you and may offer additional benefits, such as a countdown clock that updates in real time, audio and/or visual alerts, graphic design suited for the theme of the event and precision beyond days.