How to convert a given ordinal number (from Excel) to a date

The offset in Excel is the number of days since 1900/01/01, with 1 being the first of January 1900, so add the number of days as a timedelta to 1899/12/31:

from datetime import datetime, timedelta

def from_excel_ordinal(ordinal: float, _epoch0=datetime(1899, 12, 31)) -> datetime:
    if ordinal >= 60:
        ordinal -= 1  # Excel leap year bug, 1900 is not a leap year!
    return (_epoch0 + timedelta(days=ordinal)).replace(microsecond=0)

You have to adjust the ordinal by one day for any date after 1900/02/28; Excel has inherited a leap year bug from Lotus 1-2-3 and treats 1900 as a leap year. The code above returns datetime(1900, 2, 28, 0, 0) for both 59 and 60 to correct for this, with fractional values in the range [59.0 - 61.0) all being a time between 00:00:00.0 and 23:59:59.999999 on that day.

The above also supports serials with a fraction to represent time, but since Excel doesn't support microseconds those are dropped.

from datetime import datetime, timedelta

def from_excel_ordinal(ordinal, epoch=datetime(1900, 1, 1)):
    # Adapted from above, thanks to @Martijn Pieters 

    if ordinal > 59:
        ordinal -= 1  # Excel leap year bug, 1900 is not a leap year!
    inDays = int(ordinal)
    frac = ordinal - inDays
    inSecs = int(round(frac * 86400.0))

    return epoch + timedelta(days=inDays - 1, seconds=inSecs) # epoch is day 1

excelDT = 42548.75001           # Float representation of 27/06/2016  6:00:01 PM in Excel format  
pyDT = from_excel_ordinal(excelDT)

The above answer is fine for just a date value, but here I extend the above solution to include time and return a datetime values as well.

I would recomment the following:

import pandas as pd

def convert_excel_time(excel_time):

    return pd.to_datetime('1900-01-01') + pd.to_timedelta(excel_time,'D')

Or

import datetime

def xldate_to_datetime(xldate):
    temp = datetime.datetime(1900, 1, 1)
    delta = datetime.timedelta(days=xldate)
    return temp+delta

Is taken from https://gist.github.com/oag335/9959241