How to Add Days To A Date in Python

Last Updated on March 3, 2022 by Jay

This tutorial will show you how to add and subtract days to/from a date variable in Python and pandas.

We often use the datetime class to represent date and time related data. Datetime offers many convenient functions; however, we can’t intuitively add or subtract numbers from a datetime object. We need to use the timedelta object instead.

Let’s take a look at the following example:

import datetime as dt

tdy = dt.datetime.today()
print(tdy)
2022-03-02 23:41:44.287343

If we try to add 10 to the tdy variable, we’ll get the following error message:

tdy + 10

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
~\AppData\Local\Temp/ipykernel_29580/2199066677.py in <module>
----> 1 tdy + 10

TypeError: unsupported operand type(s) for +: 'datetime.datetime' and 'int'

Add Days to A Date

We need to use the datetime.timedelta object to model number of days.

tdy + dt.timedelta(days = 10)
datetime.datetime(2022, 3, 12, 23, 41, 44, 287343)

The maximum unit for a timedelta object is weeks, but it’s easier to use days in many cases. To model months or years, we can do something like this:

month = dt.timedelta(days = 30)
year = dt.timedelta(days = 365)

month * 3
datetime.timedelta(days=90)

year * 10
datetime.timedelta(days=3650)

tdy + month * 3
datetime.datetime(2022, 5, 31, 23, 41, 44, 287343)

tdy + year * 10
datetime.datetime(2032, 2, 28, 23, 41, 44, 287343)

Subtract Days from A Date

We can also subtract a certain number of days from a date easily using timedelta object:

tdy - year * 10
datetime.datetime(2012, 3, 4, 23, 41, 44, 287343)

Unfortunately, datetime has its limitations and can’t model exact months or years easily. Another 3rd party module dateutil can do that, which will be for another topic.

Add Days to A Date Column in Python Pandas

Let’s look at the following simple pandas dataframe containing just 1 date column. We specify the data type is M8[ns], or datetime64[ns].

import pandas as pd

df = pd.DataFrame(
{'date':['2021-12-01', '2022-01-01','2022-02-01','2022-03-01','2022-04-01','2022-05-01']}, 
dtype='<M8[ns]')


          date
0	2021-12-01
1	2022-01-01
2	2022-02-01
3	2022-03-01
4	2022-04-01
5	2022-05-01

We can use the timedelta object again to add or subtract days from a pandas dataframe column:

df['date'] + dt.timedelta(days = 10)

0   2021-12-11
1   2022-01-11
2   2022-02-11
3   2022-03-11
4   2022-04-11
5   2022-05-11
Name: date, dtype: datetime64[ns]