Pandas – Check if Date is the First Day of a Month

The datetime type in pandas comes with a number of useful built-in functions to get additional information about the given date. In this tutorial, we will look at how to check if a date in a pandas dataframe is the first day of a month or not with the help of some examples.

Using the is_month_start attribute

You can use is_month_start attribute on a pandas series (or a column in a dataframe) containing datetime values with the help the .dt accessor to check if each date is the start date of a month or not.

The following is the syntax –

df["Date"].dt.is_month_start

It returns a boolean pandas series where True represents that the corresponding date is the first date of the month and False represents that it’s not.

Examples

Let’s now look at some examples of using the above syntax.

First, we will create a sample dataframe to apply the above method.

import pandas as pd

# create a dataframe
df = pd.DataFrame({
    "Date": pd.date_range("2023-03-01", "2023-03-10"),
    "Sales": [10, 12, 7, 17, 21, 5, 11, 13, 14, 8]
})

# display the dataframe
df

Output:

Here, we created a dataframe with the sales data for an ecommerce website for the first 10 days of March 2023. Notice, we used the pandas date_range() function to get datetime values from “2023-03-01” to “2023-03-10” (both inclusive).

Let’s now check whether the dates in the “Date” represent the first day of a month or not.

df["Date"].dt.is_month_start

Output:

0     True
1    False
2    False
3    False
4    False
5    False
6    False
7    False
8    False
9    False
Name: Date, dtype: bool

We get a pandas series of boolean values.

Let’s add the result from the is_month_start attribute as an additional column in the above dataframe.

# add new column
df["Is First Day of Month"] = df["Date"].dt.is_month_start
# display the dataframe
df

Output:

You might also be interested in –

• Check if a DataFrame column is of datetime dtype in Pandas
• Get Rows using Datetime Index in Pandas
• Pandas – Add Days to Date (With Examples)
• Pandas – How to Create a date range?
• Pandas – Get only date from datetime
• Pandas – Get Month from Date