Age from birthdate in python

python

prompt-engineering

functions

datetime

byAnton Shumikhin·Jan 29, 2025

Here's an elegant one-liner using Python's datetime module to calculate age:

from datetime import datetime

# Assuming birthdate is a datetime object
age = datetime.now().year - birthdate.year - ((datetime.now().month, datetime.now().day) < (birthdate.month, birthdate.day))

This swiftly computes the age by factoring in whether the birthday has happened this year. After all, a year is not up until the party's over!

Age calculation considering leap years

Factoring in leap years

When working with leap years, you might feel like you've taken a leap of faith. After all, birthdays on February 29 present a unique challenge:

def calculate_age(birthdate):
    today = datetime.now().date()
    age = today.year - birthdate.year - ((today.month, today.day) < (birthdate.month, birthdate.day))

    # In the spirit of every-four-years, handle Leap Day Birthdays!
    if birthdate.month == 2 and birthdate.day == 29:
        try:
            leap_year_birthday = birthdate.replace(year=today.year)
        except ValueError:
            # If not leap year, we "round down" to Feb 28
            leap_year_birthday = birthdate.replace(year=today.year, day=28)

        if today < leap_year_birthday:
            age -= 1  # We circle back to this birthday, the party isn't over yet!
    return age

Timezones: more than just jet lag

In a world spinning round (24 timezones!), your date calculations need to keep the pace. Make sure your datetime dances to the right rhythm:

from datetime import datetime
import pytz

def calculate_age_with_timezone(birthdate, timezone_name):
    timezone = pytz.timezone(timezone_name)
    now_with_timezone = datetime.now(timezone)  # +1 for global thinking!
    return now_with_timezone.year - birthdate.year - ((now_with_timezone.month, now_with_timezone.day) < (birthdate.month, birthdate.day))

Practical visualisation

Imagine that each year is a marker on a measuring tape📏:

Start (Birthdate): 2000-01-01 (⏳beginning)
Now (Today): 2023-03-25 (⌛end)

The age calculation translates like so:

from datetime import date

birthdate = date(2000, 1, 1)
today = date.today()
age = today.year - birthdate.year - ((today.month, today.day) < (birthdate.month, birthdate.day))

Unrolling the tape measures out the years:

⏳---1Y---2Y---...---22Y---23Y ⌛

Here, ⏳ is the birthdate and ⌛ represents today's date. The markers (-) are the years elapsed between the two. The mathematical calculation unveils the distance covered on this tape: the person's age in years.

Advanced tricks and tips

Dates and strings: Playing well together

Handling dates can be like herding cats if they come in all shapes and sizes. Here's a solution for dealing stylishly with string-formatted birthdates:

from datetime import datetime

def convert_and_calculate_age(birthdate_str, date_format='%Y-%m-%d'):
    birthdate = datetime.strptime(birthdate_str, date_format)  # My cats speak `%Y-%m-%d` language!
    # (days lived) // (days in a year) = age. Simple math, right?
    return (datetime.now() - birthdate).days // 365

Precise age with relativedelta

For those who like the consolation of precision, balance the relativedelta beam from python-dateutil:

from dateutil.relativedelta import relativedelta

def precise_age(birthdate):
    today = datetime.now()
    delta = relativedelta(today, birthdate)  # it takes two to make an age go right!
    return delta.years

Age with Django's DateField

Django enthusiasts, here's an age calculation snippet right out of the Django model recipe book:

from django.db import models
from datetime import datetime

class Person(models.Model):
    birthdate = models.DateField()

    def age(self):
        today = datetime.now().date()
        # Life's not complete without a birthday!
        return today.year - self.birthdate.year - ((today.month, today.day) < (self.birthdate.month, self.birthdate.day))

Include UTC time

For those who answer to a higher time, UTC is the only language spoken. Translate your dates well:

from datetime import datetime

def calculate_age_utc(birthdate):
    utc_now = datetime.utcnow()  # UTC says... tick tock on the clock!
    return utc_now.year - birthdate.year - ((utc_now.month, utc_now.day) < (birthdate.month, birthdate.day))