from datetime import date


def calculate_age(birthday):
    today = date.today()
    born = birthday
    try:
        birthday = born.replace(year=today.year)
    except ValueError:
        birthday = born.replace(year=today.year, month=born.month + 1, day=1)

    age = today.year - born.year
    if birthday > today:
        age -= 1
    return age