How to calculate days until a date
Short answer: subtract calendar dates, not hours. Days left = target date minus today's date. If today is March 1 and your trip is May 17, that is 30 (rest of March) + 30 (April) + 17 = 77 days.
1. Why apps disagree (74 vs 77)
Reviewers of popular countdown apps complain that the app "said 74 days when it was really 77". That happens when an app counts 24-hour blocks from the current time and rounds down, or stores the date in a different time zone. A trip at midnight, a daylight saving change or a phone that switched time zones can each knock a day off.
2. Count it by hand
- Write down today's date and the target date.
- Count the days left in this month, add the full months in between, add the day of the target month.
- Check: D-1 should be the day before the event, D-Day the day itself.
3. Days since a past date
The same rule works backwards: today minus the past date. 412 days since a start date means 412 calendar days have passed.
Doing it with Nearday
Nearday counts by calendar day, so the number matches what you count on a calendar. Upcoming events sort nearest first, past events keep counting up, and yearly events like birthdays roll over by themselves. No sign-up, nothing locked.
FAQ
How do I count the days between two dates?
Subtract the calendar dates: target date minus today's date. Do not count 24-hour blocks from the current time.
Why do two countdown apps show different numbers?
One counts calendar days, the other counts hours divided by 24 and rounds down. Time zones and daylight saving make the gap bigger.
Is the target day itself included?
In a normal countdown, no. D-1 is the day before, D-Day is the day itself.