Excel Calculate Months From Two Dates

Calculate months between two dates with precision – just like Excel’s DATEDIF function

Complete Guide: How to Calculate Months Between Two Dates in Excel

Calculating the difference between two dates in months is a common requirement in financial modeling, project management, and data analysis. While Excel doesn’t have a dedicated “MONTHSDIFF” function, you can achieve this using several methods with varying levels of precision.

The DATEDIF Function: Excel’s Hidden Gem

The DATEDIF function (Date + Dif) is Excel’s most powerful tool for date calculations, though it’s not officially documented in newer versions. This function can calculate the difference between two dates in years, months, or days.

Why Use DATEDIF?

• Handles all edge cases (leap years, month-end dates)
• More accurate than simple subtraction methods
• Works in all Excel versions (2007 and later)
• Supports multiple calculation modes

DATEDIF Syntax and Parameters

The function uses this structure:

=DATEDIF(start_date, end_date, unit)

Unit Parameter	Description	Example Return
“Y”	Complete years between dates	For 1/1/2020 to 1/1/2023 → 3
“M”	Complete months between dates	For 1/1/2023 to 3/15/2023 → 2
“D”	Days between dates	For 1/1/2023 to 1/15/2023 → 14
“MD”	Days remaining after complete months	For 1/1/2023 to 3/15/2023 → 14
“YM”	Months remaining after complete years	For 1/1/2020 to 3/15/2023 → 2
“YD”	Days remaining after complete years	For 1/1/2020 to 3/15/2023 → 73

Practical Examples of DATEDIF

1. Basic Month Calculation

To get the total months between two dates (rounding down):

=DATEDIF(A1, B1, "m")

Where A1 contains the start date and B1 contains the end date.

2. Exact Month Calculation (Including Partial Months)

For more precise calculations that account for partial months:

=DATEDIF(A1, B1, "m") + (DAY(B1) >= DAY(A1)) * 1

This formula adds 1 month if the end day is greater than or equal to the start day.

3. Years and Months Separately

To get both years and months between dates:

=DATEDIF(A1, B1, "y") & " years and " & DATEDIF(A1, B1, "ym") & " months"

4. Age Calculation

Perfect for calculating someone’s age in years, months, and days:

=DATEDIF(A1, TODAY(), "y") & " years, " & DATEDIF(A1, TODAY(), "ym") & " months, " & DATEDIF(A1, TODAY(), "md") & " days"

Alternative Methods for Date Calculations

While DATEDIF is the most reliable method, Excel offers other approaches:

1. Using YEARFRAC Function

The YEARFRAC function calculates the fraction of a year between two dates, which you can then multiply by 12:

=YEARFRAC(A1, B1, 1) * 12

Note: The third parameter (1) specifies the day count basis (actual/actual).

YEARFRAC Limitations

YEARFRAC may give slightly different results than DATEDIF because:

• It calculates fractional years first, then converts to months
• Different day count bases can affect results
• Less precise for partial month calculations

2. Simple Subtraction Method

For quick approximations (less accurate):

=((YEAR(B1)-YEAR(A1))*12)+MONTH(B1)-MONTH(A1)

This doesn’t account for day differences within months.

3. Using EDATE Function

EDATE adds months to a date, which you can use in combination with other functions:

=MONTH(EDATE(A1, DATEDIF(A1, B1, "m")) - B1)

Handling Edge Cases

Date calculations can get tricky with these scenarios:

1. Month-End Dates

When calculating between month-end dates (like 1/31 to 2/28), Excel handles this intelligently:

=DATEDIF("1/31/2023", "2/28/2023", "m")  // Returns 1

2. Negative Results

If the end date is before the start date, DATEDIF returns a #NUM! error. Handle this with IF:

=IF(B1>A1, DATEDIF(A1, B1, "m"), "Invalid date range")

3. Leap Years

DATEDIF automatically accounts for leap years in day calculations:

=DATEDIF("2/28/2023", "2/28/2024", "d")  // Returns 365
=DATEDIF("2/28/2024", "2/28/2025", "d")  // Returns 366

Real-World Applications

Industry	Use Case	Example Formula
Finance	Loan term calculation	=DATEDIF(start_date, end_date, “m”)/12
HR	Employee tenure	=DATEDIF(hire_date, TODAY(), “y”) & ” years”
Project Management	Project duration	=DATEDIF(start_date, end_date, “m”) & ” months”
Education	Course duration	=DATEDIF(start_date, end_date, “d”)/30 & ” months”
Legal	Contract periods	=DATEDIF(sign_date, expiry_date, “m”)

Common Mistakes to Avoid

1. Assuming all months have equal length: Not accounting for varying month lengths (28-31 days) can lead to inaccurate results.
2. Ignoring date formats: Ensure cells are formatted as dates, not text, to avoid calculation errors.
3. Forgetting about time zones: If working with international dates, consider time zone differences.
4. Using simple subtraction: (End date – Start date)/30 is not reliable for month calculations.
5. Not handling errors: Always include error handling for invalid date ranges.

Advanced Techniques

1. Creating a Date Difference Table

Generate a table showing years, months, and days between dates:

=DATEDIF(A1, B1, "y") & " years, " &
DATEDIF(A1, B1, "ym") & " months, " &
DATEDIF(A1, B1, "md") & " days"

2. Dynamic Date Ranges

Calculate months between today and a future/past date:

=DATEDIF(TODAY(), B1, "m")

3. Conditional Formatting

Highlight dates that are within 3 months of today:

1. Select your date range
2. Go to Conditional Formatting > New Rule
3. Use formula: =DATEDIF(TODAY(),A1,"m")<=3
4. Set your desired format

4. Array Formulas for Multiple Dates

Calculate months between multiple date pairs in columns A and B:

{=DATEDIF(A1:A100, B1:B100, "m")}

Enter as an array formula with Ctrl+Shift+Enter in older Excel versions.

Excel vs. Other Tools

Tool	Month Calculation Method	Accuracy	Ease of Use
Excel (DATEDIF)	=DATEDIF(start,end,"m")	⭐⭐⭐⭐⭐	⭐⭐⭐⭐
Google Sheets	=DATEDIF(start,end,"m")	⭐⭐⭐⭐⭐	⭐⭐⭐⭐
JavaScript	Complex date math required	⭐⭐⭐⭐	⭐⭐
Python (pandas)	df['months'] = (df['end'] - df['start'])/np.timedelta64(1,'M')	⭐⭐⭐⭐	⭐⭐⭐
SQL	DATEDIFF(month, start, end)	⭐⭐⭐	⭐⭐⭐

Best Practices for Date Calculations

1. Always validate dates: Use ISDATE or Data Validation to ensure inputs are valid dates.
2. Document your formulas: Add comments explaining complex date calculations.
3. Consider time zones: If working with international data, standardize on UTC or include time zone information.
4. Test edge cases: Always test with:
   • Month-end dates (31st)
   • Leap days (February 29)
   • Date reversals (end before start)
   • Very large date ranges
5. Use named ranges: For better readability in complex workbooks.
6. Consider fiscal years: If your organization uses a non-calendar fiscal year, adjust calculations accordingly.
7. Format consistently: Use the same date format throughout your workbook.

Microsoft Official Documentation: DATEDIF Function

Microsoft's official (though undocumented) reference for the DATEDIF function with examples.

NIST Time and Frequency Division

National Institute of Standards and Technology resources on date and time calculations.

Stanford University: Date Functions in Databases

Academic resource comparing date functions across different database systems.

Frequently Asked Questions

Why does Excel show ###### in my date cells?

This typically indicates either:

• The column isn't wide enough to display the date format
• The cell contains a negative date value (before 1/1/1900 in Windows Excel)
• An invalid date calculation result

Solution: Widen the column or check your date values.

How does Excel store dates internally?

Excel stores dates as sequential serial numbers where:

• January 1, 1900 = 1 (Windows) or January 1, 1904 = 0 (Mac)
• Each day increments the number by 1
• Times are stored as fractional portions of a day

This system allows date arithmetic operations.

Can I calculate business months (excluding weekends)?

Yes, but it requires a more complex approach:

=SUMPRODUCT(--(WEEKDAY(ROW(INDIRECT(A1&":"&B1)))<>1),
               --(WEEKDAY(ROW(INDIRECT(A1&":"&B1)))<>7))/30

Or use the NETWORKDAYS function for business days and convert to months.

Why do I get different results in Excel vs. Google Sheets?

While both support DATEDIF, differences can occur due to:

• Different default date systems (1900 vs. 1904)
• Handling of two-digit years differently
• Different day count conventions
• Time zone handling in web apps

For critical calculations, always verify results in both platforms.

How can I calculate the number of weekdays between dates?

Use the NETWORKDAYS function:

=NETWORKDAYS(A1, B1)

For more control over holidays:

=NETWORKDAYS(A1, B1, holidays_range)

Conclusion

Mastering date calculations in Excel—particularly calculating months between dates—is an essential skill for anyone working with temporal data. The DATEDIF function, while not officially documented in newer Excel versions, remains the most reliable tool for these calculations. By understanding its various parameters and combining it with other Excel functions, you can handle virtually any date-based calculation requirement.

Remember these key points:

• DATEDIF is case-sensitive with its unit parameters
• Always test with edge cases like month-end dates
• Consider whether to include the end date in your calculation
• Document complex date formulas for future reference
• For mission-critical calculations, cross-verify with alternative methods

As you become more comfortable with these techniques, you'll find countless applications in financial modeling, project planning, data analysis, and business reporting. The ability to accurately calculate time periods is fundamental to making data-driven decisions in nearly every professional field.