Python Pandas - Indicate whether the date in DateTimeIndex is the last day of the month

To check whether dates in a DateTimeIndex correspond to the last day of their respective months, use the is_month_end property. This returns a boolean array indicating which dates fall on month-end dates.

Syntax

DateTimeIndex.is_month_end

Creating a DateTimeIndex

First, let's create a DateTimeIndex with various dates ?

import pandas as pd

# Create DateTimeIndex with 15-day intervals
datetimeindex = pd.date_range('2021-9-15 06:40:35', periods=6, tz='Australia/Adelaide', freq='15D')

print("DateTimeIndex...")
print(datetimeindex)

DateTimeIndex...
DatetimeIndex(['2021-09-15 06:40:35+09:30', '2021-09-30 06:40:35+09:30',
               '2021-10-15 06:40:35+10:30', '2021-10-30 06:40:35+10:30',
               '2021-11-14 06:40:35+10:30', '2021-11-29 06:40:35+10:30'],
              dtype='datetime64[ns, Australia/Adelaide]', freq='15D')

Checking Month-End Dates

Use the is_month_end property to identify which dates are the last day of their month ?

import pandas as pd

datetimeindex = pd.date_range('2021-9-15 06:40:35', periods=6, tz='Australia/Adelaide', freq='15D')

# Check which dates are month-end dates
month_end_check = datetimeindex.is_month_end
print("Is month end?")
print(month_end_check)

# Display frequency for reference
print("\nDateTimeIndex frequency:")
print(datetimeindex.freq)

Is month end?
[False  True False False False False]

DateTimeIndex frequency:
<15 * Days>

Example with Different Dates

Let's create another example with specific month-end dates ?

import pandas as pd

# Create dates including some month-end dates
dates = ['2023-01-31', '2023-02-15', '2023-02-28', '2023-03-31', '2023-04-15']
datetimeindex = pd.to_datetime(dates)

print("Dates:")
for i, date in enumerate(datetimeindex):
    print(f"{date.strftime('%Y-%m-%d')}: {datetimeindex.is_month_end[i]}")

Dates:
2023-01-31: True
2023-02-15: False
2023-02-28: True
2023-03-31: True
2023-04-15: False

Key Points

• Returns a boolean array with True for month-end dates
• Works with timezone-aware DateTimeIndex objects
• Considers the actual last day of each month (handles February, leap years, etc.)
• Useful for financial and time-series analysis

Conclusion

The is_month_end property provides an efficient way to identify month-end dates in a DateTimeIndex. It returns a boolean array that can be used for filtering or conditional operations in time-series data analysis.