Calculate Age from Date of Birth in Python: Simple Guide

To calculate age from date of birth in Python, use the datetime module to get today's date and subtract the birth date. Then adjust the result to account for whether the birthday has occurred this year.

Syntax

Use the datetime module to work with dates. The main parts are:

• datetime.date.today(): gets today's date.
• datetime.date(year, month, day): creates a date object for the birth date.
• Subtract birth year from current year, then adjust if birthday hasn't happened yet this year.

python

from datetime import date

def calculate_age(birthdate):
    today = date.today()
    age = today.year - birthdate.year
    if (today.month, today.day) < (birthdate.month, birthdate.day):
        age -= 1
    return age

Example

This example shows how to calculate the age of a person born on July 20, 1990.

python

from datetime import date

def calculate_age(birthdate):
    today = date.today()
    age = today.year - birthdate.year
    if (today.month, today.day) < (birthdate.month, birthdate.day):
        age -= 1
    return age

birth_date = date(1990, 7, 20)
age = calculate_age(birth_date)
print(f"Age is: {age}")

Output

Age is: 33

Common Pitfalls

Common mistakes include:

• Not adjusting the age if the birthday hasn't happened yet this year, which can make the age one year too high.
• Using datetime.datetime instead of datetime.date without handling time parts.
• Forgetting to import the datetime module.

python

from datetime import date

# Wrong way: does not check if birthday passed this year

def wrong_calculate_age(birthdate):
    today = date.today()
    return today.year - birthdate.year

# Right way: adjusts if birthday not passed

def right_calculate_age(birthdate):
    today = date.today()
    age = today.year - birthdate.year
    if (today.month, today.day) < (birthdate.month, birthdate.day):
        age -= 1
    return age

Quick Reference

Remember these tips when calculating age:

• Use datetime.date for dates without time.
• Subtract birth year from current year.
• Check if birthday has occurred this year to adjust age.
• Use tuple comparison for month and day to simplify logic.

Key Takeaways

Use the datetime module's date class to handle dates simply.

Calculate age by subtracting birth year from current year and adjust if birthday hasn't occurred yet this year.

Always compare month and day as a tuple to decide if you should subtract one from age.

Avoid using datetime.datetime if you only need date parts to keep code clean.

Test your function with birthdays before and after today's date to ensure accuracy.