Age from birthdate in python

Unfortunately, you cannot just use timedelata as the largest unit it uses is day and leap years will render you calculations invalid. Therefore, let’s find number of years then adjust by one if the last year isn’t full:

from datetime import date
birth_date = date(1980, 5, 26)
years = date.today().year - birth_date.year
if (datetime.now() - birth_date.replace(year=datetime.now().year)).days >= 0:
    age = years
else:
    age = years - 1

Upd:

This solution really causes an exception when Feb, 29 comes into play. Here’s correct check:

from datetime import date
birth_date = date(1980, 5, 26)
today = date.today()
years = today.year - birth_date.year
if all((x >= y) for x,y in zip(today.timetuple(), birth_date.timetuple()):
   age = years
else:
   age = years - 1

Upd2:

Calling multiple calls to now() a performance hit is ridiculous, it does not matter in all but extremely special cases. The real reason to use a variable is the risk of data incosistency.

The classic gotcha in this scenario is what to do with people born on the 29th day of February. Example: you need to be aged 18 to vote, drive a car, buy alcohol, etc … if you are born on 2004-02-29, what is the first day that you are permitted to do such things: 2022-02-28, or 2022-03-01? AFAICT, mostly the first, but a few killjoys might say the latter.

Here’s code that caters for the 0.068% (approx) of the population born on that day:

def age_in_years(from_date, to_date, leap_day_anniversary_Feb28=True):
    age = to_date.year - from_date.year
    try:
        anniversary = from_date.replace(year=to_date.year)
    except ValueError:
        assert from_date.day == 29 and from_date.month == 2
        if leap_day_anniversary_Feb28:
            anniversary = datetime.date(to_date.year, 2, 28)
        else:
            anniversary = datetime.date(to_date.year, 3, 1)
    if to_date < anniversary:
        age -= 1
    return age

if __name__ == "__main__":
    import datetime

    tests = """

    2004  2 28 2010  2 27  5 1
    2004  2 28 2010  2 28  6 1
    2004  2 28 2010  3  1  6 1

    2004  2 29 2010  2 27  5 1
    2004  2 29 2010  2 28  6 1
    2004  2 29 2010  3  1  6 1

    2004  2 29 2012  2 27  7 1
    2004  2 29 2012  2 28  7 1
    2004  2 29 2012  2 29  8 1
    2004  2 29 2012  3  1  8 1

    2004  2 28 2010  2 27  5 0
    2004  2 28 2010  2 28  6 0
    2004  2 28 2010  3  1  6 0

    2004  2 29 2010  2 27  5 0
    2004  2 29 2010  2 28  5 0
    2004  2 29 2010  3  1  6 0

    2004  2 29 2012  2 27  7 0
    2004  2 29 2012  2 28  7 0
    2004  2 29 2012  2 29  8 0
    2004  2 29 2012  3  1  8 0

    """

    for line in tests.splitlines():
        nums = [int(x) for x in line.split()]
        if not nums:
            print
            continue
        datea = datetime.date(*nums[0:3])
        dateb = datetime.date(*nums[3:6])
        expected, anniv = nums[6:8]
        age = age_in_years(datea, dateb, anniv)
        print datea, dateb, anniv, age, expected, age == expected

Here’s the output:

2004-02-28 2010-02-27 1 5 5 True
2004-02-28 2010-02-28 1 6 6 True
2004-02-28 2010-03-01 1 6 6 True

2004-02-29 2010-02-27 1 5 5 True
2004-02-29 2010-02-28 1 6 6 True
2004-02-29 2010-03-01 1 6 6 True

2004-02-29 2012-02-27 1 7 7 True
2004-02-29 2012-02-28 1 7 7 True
2004-02-29 2012-02-29 1 8 8 True
2004-02-29 2012-03-01 1 8 8 True

2004-02-28 2010-02-27 0 5 5 True
2004-02-28 2010-02-28 0 6 6 True
2004-02-28 2010-03-01 0 6 6 True

2004-02-29 2010-02-27 0 5 5 True
2004-02-29 2010-02-28 0 5 5 True
2004-02-29 2010-03-01 0 6 6 True

2004-02-29 2012-02-27 0 7 7 True
2004-02-29 2012-02-28 0 7 7 True
2004-02-29 2012-02-29 0 8 8 True
2004-02-29 2012-03-01 0 8 8 True

from datetime import date

def calculate_age(born):
    today = date.today()
    try: 
        birthday = born.replace(year=today.year)
    except ValueError: # raised when birth date is February 29 and the current year is not a leap year
        birthday = born.replace(year=today.year, month=born.month+1, day=1)
    if birthday > today:
        return today.year - born.year - 1
    else:
        return today.year - born.year

Update: Use Danny’s solution, it’s better

As I did not see the correct implementation, I recoded mine this way…

    def age_in_years(from_date, to_date=datetime.date.today()):
  if (DEBUG):
    logger.debug("def age_in_years(from_date='%s', to_date='%s')" % (from_date, to_date))

  if (from_date>to_date): # swap when the lower bound is not the lower bound
    logger.debug('Swapping dates ...')
    tmp = from_date
    from_date = to_date
    to_date = tmp

  age_delta = to_date.year - from_date.year
  month_delta = to_date.month - from_date.month
  day_delta = to_date.day - from_date.day

  if (DEBUG):
    logger.debug("Delta's are : %i  / %i / %i " % (age_delta, month_delta, day_delta))

  if (month_delta>0  or (month_delta==0 and day_delta>=0)): 
    return age_delta 

  return (age_delta-1)

Assumption of being “18” on the 28th of Feb when born on the 29th is just wrong.
Swapping the bounds can be left out … it is just a personal convenience for my code 🙂

from datetime import date

days_in_year = 365.2425    
age = int((date.today() - birth_date).days / days_in_year)

In Python 3, you could perform division on datetime.timedelta:

from datetime import date, timedelta

age = (date.today() - birth_date) // timedelta(days=365.2425)

import datetime

def age(date_of_birth):
    if date_of_birth > datetime.date.today().replace(year = date_of_birth.year):
        return datetime.date.today().year - date_of_birth.year - 1
    else:
        return datetime.date.today().year - date_of_birth.year

In your case:

import datetime

# your model
def age(self):
    if self.birthdate > datetime.date.today().replace(year = self.birthdate.year):
        return datetime.date.today().year - self.birthdate.year - 1
    else:
        return datetime.date.today().year - self.birthdate.year

from datetime import date

def age(birth_date):
    today = date.today()
    y = today.year - birth_date.year
    if today.month < birth_date.month or today.month == birth_date.month and today.day < birth_date.day:
        y -= 1
    return y

The simplest way is using python-dateutil

import datetime

import dateutil

def birthday(date):
    # Get the current date
    now = datetime.datetime.utcnow()
    now = now.date()

    # Get the difference between the current date and the birthday
    age = dateutil.relativedelta.relativedelta(now, date)
    age = age.years

    return age

Here is a solution to find age of a person as either years or months or days.

Lets say a person’s date of birth is 2012-01-17T00:00:00
Therefore, his age on 2013-01-16T00:00:00 will be 11 months

or if he is born on 2012-12-17T00:00:00,
his age on 2013-01-12T00:00:00 will be 26 days

or if he is born on 2000-02-29T00:00:00,
his age on 2012-02-29T00:00:00 will be 12 years

You will need to import datetime.

Here is the code:

def get_person_age(date_birth, date_today):

"""
At top level there are three possibilities : Age can be in days or months or years.
For age to be in years there are two cases: Year difference is one or Year difference is more than 1
For age to be in months there are two cases: Year difference is 0 or 1
For age to be in days there are 4 possibilities: Year difference is 1(20-dec-2012 - 2-jan-2013),
                                                 Year difference is 0, Months difference is 0 or 1
"""
years_diff = date_today.year - date_birth.year
months_diff = date_today.month - date_birth.month
days_diff = date_today.day - date_birth.day
age_in_days = (date_today - date_birth).days

age = years_diff
age_string = str(age) + " years"

# age can be in months or days.
if years_diff == 0:
    if months_diff == 0:
        age = age_in_days
        age_string = str(age) + " days"
    elif months_diff == 1:
        if days_diff < 0:
            age = age_in_days
            age_string = str(age) + " days"
        else:
            age = months_diff
            age_string = str(age) + " months"
    else:
        if days_diff < 0:
            age = months_diff - 1
        else:
            age = months_diff
        age_string = str(age) + " months"
# age can be in years, months or days.
elif years_diff == 1:
    if months_diff < 0:
        age = months_diff + 12
        age_string = str(age) + " months" 
        if age == 1:
            if days_diff < 0:
                age = age_in_days
                age_string = str(age) + " days" 
        elif days_diff < 0:
            age = age-1
            age_string = str(age) + " months"
    elif months_diff == 0:
        if days_diff < 0:
            age = 11
            age_string = str(age) + " months"
        else:
            age = 1
            age_string = str(age) + " years"
    else:
        age = 1
        age_string = str(age) + " years"
# The age is guaranteed to be in years.
else:
    if months_diff < 0:
        age = years_diff - 1
    elif months_diff == 0:
        if days_diff < 0:
            age = years_diff - 1
        else:
            age = years_diff
    else:
        age = years_diff
    age_string = str(age) + " years"

if age == 1:
    age_string = age_string.replace("years", "year").replace("months", "month").replace("days", "day")

return age_string

Some extra functions used in the above codes are:

def get_todays_date():
    """
    This function returns todays date in proper date object format
    """
    return datetime.now()

And

def get_date_format(str_date):
"""
This function converts string into date type object
"""
str_date = str_date.split("T")[0]
return datetime.strptime(str_date, "%Y-%m-%d")

Now, we have to feed get_date_format() with the strings like 2000-02-29T00:00:00

It will convert it into the date type object which is to be fed to get_person_age(date_birth, date_today).

The function get_person_age(date_birth, date_today) will return age in string format.

If you’re looking to print this in a page using django templates, then the following might be enough:

{{ birth_date|timesince }}

Expanding on Danny’s Solution, but with all sorts of ways to report ages for younger folk (note, today is datetime.date(2015,7,17)):

def calculate_age(born):
    '''
        Converts a date of birth (dob) datetime object to years, always rounding down.
        When the age is 80 years or more, just report that the age is 80 years or more.
        When the age is less than 12 years, rounds down to the nearest half year.
        When the age is less than 2 years, reports age in months, rounded down.
        When the age is less than 6 months, reports the age in weeks, rounded down.
        When the age is less than 2 weeks, reports the age in days.
    '''
    today = datetime.date.today()
    age_in_years = today.year - born.year - ((today.month, today.day) < (born.month, born.day))
    months = (today.month - born.month - (today.day < born.day)) %12
    age = today - born
    age_in_days = age.days
    if age_in_years >= 80:
        return 80, 'years or older'
    if age_in_years >= 12:
        return age_in_years, 'years'
    elif age_in_years >= 2:
        half = 'and a half ' if months > 6 else ''
        return age_in_years, '%syears'%half
    elif months >= 6:
        return months, 'months'
    elif age_in_days >= 14:
        return age_in_days/7, 'weeks'
    else:
        return age_in_days, 'days'

Sample code:

print '%d %s' %calculate_age(datetime.date(1933,6,12)) # >=80 years
print '%d %s' %calculate_age(datetime.date(1963,6,12)) # >=12 years
print '%d %s' %calculate_age(datetime.date(2010,6,19)) # >=2 years
print '%d %s' %calculate_age(datetime.date(2010,11,19)) # >=2 years with half
print '%d %s' %calculate_age(datetime.date(2014,11,19)) # >=6 months
print '%d %s' %calculate_age(datetime.date(2015,6,4)) # >=2 weeks
print '%d %s' %calculate_age(datetime.date(2015,7,11)) # days old

80 years or older
52 years
5 years
4 and a half years
7 months
6 weeks
7 days

As suggested by @[Tomasz Zielinski] and @Williams python-dateutil can do it just 5 lines.

from dateutil.relativedelta import *
from datetime import date
today = date.today()
dob = date(1982, 7, 5)
age = relativedelta(today, dob)

>>relativedelta(years=+33, months=+11, days=+16)`

Slightly modified Danny’s solution for easier reading and understanding

    from datetime import date

    def calculate_age(birth_date):
        today = date.today()
        age = today.year - birth_date.year
        full_year_passed = (today.month, today.day) < (birth_date.month, birth_date.day)
        if not full_year_passed:
            age -= 1
        return age

Extend to Danny W. Adair Answer, to get month also

def calculate_age(b):
    t = date.today()
    c = ((t.month, t.day) < (b.month, b.day))
    c2 = (t.day< b.day)
    return t.year - b.year - c,c*12+t.month-b.month-c2

import datetime

Todays date

td=datetime.datetime.now().date() 

Your birthdate

bd=datetime.date(1989,3,15)

Your age

age_years=int((td-bd).days /365.25)

You can use Python 3 to do all this. Just run the following code and see.

# Creating a variables:

greeting = "Hello, "
name = input("what is your name?")
birth_year = input("Which year you were born?")
response = "Your age is "

# Converting string variable to int:

calculation = 2020 - int(birth_year) 


# Printing:

print(f'{greeting}{name}. {response}{calculation}')

serializers.py

age = serializers.SerializerMethodField('get_age')

class Meta:
    model = YourModel
    fields = [..,'','birthdate','age',..]


import datetime

def get_age(self, instance):
    return datetime.datetime.now().year - instance.birthdate.year

A slightly more elegant solution than @DannyWAdairs solution might be to work with the .timetuple() method ^[Python-doc]:

from datetime import date

def calculate_age(born):
    today = date.today()
    return today.year - born.year - (today.timetuple()[1:3] < born.timetuple()[1:3])

You can easily use this to generalize this further to increase its granularity to seconds, such that the age increments if it is greater than or equal to the number of seconds of that day, if born is for example a datetime object:

from datetime import datetime

def calculate_age_with_seconds(born):
    today = datetime.now()
    return today.year - born.year - (today.timetuple()[1:6] < born.timetuple()[1:6])

This will work for born both being a date or a datetime object.