⏳ Days Until Calculator (D-Day)
How many days until Christmas, a trip, a deadline or a due date? Or how many days since something started? Enter one date and get the countdown plus milestone dates.
Milestone dates (your date as the start date)
How to use the days-until calculator
Enter one date. A future date gives you a countdown (e.g. "73 days" or D-73); a past date tells you how long ago it was, or which day number you're on (e.g. "Day 100" of a streak, a sobriety count or a relationship). The table below treats your date as a start date and lists the 100-day, 1,000-day and yearly milestones in date order, highlighting the next one coming up. Change "Count from" to count from any day other than today.
What does D-Day mean?
"D-Day" is the target day. In Korea and much of Asia, countdowns are written D-30 (30 days to go) and counts after the event D+100 (100 days since). Exam-prep apps, wedding planners and couples use this notation everywhere, so we show it alongside the plain-English count.
Day 1 or Day 0? Counting the start date
Most countdowns are simple: days remaining = target date − today. Counting since a date is where people disagree:
- Start date = Day 1 — the way streaks, "Day 100 of my diet", baby 100-day celebrations and Korean couple anniversaries are counted. Day 100 falls 99 days after the start date. If you started on January 1, Day 100 is April 10 (in a common year).
- Start date = Day 0 — the plain calendar difference ("100 days after January 1" is April 11). Legal deadlines and most date math work this way.
Yearly anniversaries are the same calendar day either way (a Feb 29 start falls on Feb 28 in common years).
Formulas
- Days until
target date − count-from date. 0 means today is the day. - Day number
count-from date − start date + 1(when the start date is Day 1) - N-day milestone
start date + (N − 1) days(Day 1 counting) orstart date + N days(Day 0 counting)
All dates are counted in whole days, so daylight saving time and time zones never cause an off-by-one error.
Popular countdowns
- Christmas & New Year's Day — the buttons jump to the next upcoming one automatically.
- Thanksgiving — the fourth Thursday of November in the US.
- 1 year ago — previews the milestone table for something that started exactly a year ago.
- For a pregnancy countdown, the due date calculator also shows weeks and trimesters.
Need the detailed gap between two arbitrary dates (months, weekdays, hours)? Use the days between dates calculator. Need "90 days from today" or "10 business days before"? Use the date calculator.
Weekday counts exclude Saturdays and Sundays only — public holidays are not removed. For legal, tax or court deadlines, follow the official rules that apply to you.