Regarding simple python date calc
YEARSEC=(12*30*24*3600)
MONTHSEC=(3600*24*30)
DAYSEC=(24*3600)
HOURSEC=3600
MINUTESEC=60

year=int(input("Please enter the year in which you were born: "))
month=int(input("Please enter the month you were born: "))
day=int(input("Please enter the day you were born: "))
hour=int(input("Please enter the hour you were born: "))
minute=int(input("Please enter the minute you were born: "))
second=int(input("Please enter the second you were born: "))

year_calc=(year*YEARSEC)
month_calc=(month*MONTHSEC)
day_calc=(day*DAYSEC)
hour_calc=(hour*HOURSEC)
minute_calc=(minute*MINUTESEC)
s=(1000000000+year_calc+month_calc+day_calc+hour_calc+minute_calc+second)


year_num=int((s/YEARSEC))
s=(s-(year_num*YEARSEC))


month_num=int((s/MONTHSEC))
s=(s-(month_num*MONTHSEC))


day_num=int((s/DAYSEC))
s=(s-(DAYSEC*day_num))

hour_num=int((s/HOURSEC))
s=(s-(HOURSEC*hour_num))

minute_num=int((s/MINUTESEC))
s=(s-(MINUTESEC*minute_num))




print("You will turn 1 000 000 000 seconds old on: %04d/%02d/%02d %02d:%02d:%02d" %(year_num,month_num,day_num,hour_num,minute_num,s))

print("You will turn 1 000 000 000 seconds old on: %04d/%02d/%02d %02d:%02d:%02d" %(year_num,month_num+1,day_num+1,hour_num,minute_num,s))

>>> import datetime
>>> birthday = datetime.datetime(1993,11,05,0,0,0)
>>> billion = birthday + datetime.timedelta(seconds=1000000000)
>>> billion.ctime()
'Mon Jul 14 01:46:40 2025'