Days until a date in Python (countdown, next birthday)

Subtract today's date from the target date and you get the number of days left. The program also has to handle two other cases: the date is today, or the date has already passed.

The program

python

from datetime import date


def countdown_message(event, target, today):
    days_left = (target - today).days
    if days_left > 1:
        return f"{event}: {days_left} days to go"
    if days_left == 1:
        return f"{event}: tomorrow!"
    if days_left == 0:
        return f"{event}: today!"
    return f"{event}: passed {-days_left} days ago"


today = date(2026, 10, 22)  # fixed so the output matches this page; use date.today() in real use

events = [
    ("New Year", date(2027, 1, 1)),
    ("Project deadline", date(2026, 10, 23)),
    ("Conference talk", date(2026, 10, 22)),
    ("Summer holiday", date(2026, 8, 3)),
]

for event, target in events:
    print(countdown_message(event, target, today))

output

New Year: 71 days to go
Project deadline: tomorrow!
Conference talk: today!
Summer holiday: passed 80 days ago

How it works

(target - today).days is positive when the target is in the future, 0 when it is today, and negative when it has passed.
The checks go from the largest number down, so each case is handled once. "1 days to go" would read badly, so 1 gets its own message.
-days_left turns a negative number such as -80 into 80 for the "ago" message.
today is passed in as an argument instead of calling date.today() inside the function. That makes the function easy to test with any date, as this page does.

Countdown to the next birthday

A birthday comes back every year. If this year's birthday has already passed, count to next year's:

python

from datetime import date


def days_to_birthday(birth, today):
    next_birthday = birth.replace(year=today.year)
    if next_birthday < today:
        next_birthday = birth.replace(year=today.year + 1)
    return (next_birthday - today).days


today = date(2026, 10, 22)  # fixed so the output matches this page; use date.today() in real use

for name, birth in [("Ada", date(1990, 12, 10)), ("Hedy", date(1985, 3, 1)), ("Linus", date(1992, 10, 22))]:
    print(f"{name}: {days_to_birthday(birth, today)} days")

output

Ada: 49 days
Hedy: 130 days
Linus: 0 days

birth.replace(year=...) keeps the month and day and changes the year. One case needs care: for a birthday on 29 February, replace() raises a ValueError in a year that is not a leap year. You can catch that and use 1 March (or 28 February) instead. The age calculator uses the same "has the birthday passed?" idea.

Countdown to a date in Python

The program

How it works

Countdown to the next birthday