Calculating Months Between Dates In Excel

Calculate the exact number of months between two dates with precision – just like Excel’s DATEDIF function

Understanding Excel’s Date Calculations

Excel stores dates as sequential serial numbers where January 1, 1900 is serial number 1. This system allows Excel to perform complex date calculations, including determining the number of months between two dates. The most powerful function for this purpose is DATEDIF, though it’s not officially documented in Excel’s function library.

Key Excel Date Functions

• DATEDIF: Calculates difference between dates in various units
• YEARFRAC: Returns fraction of year between dates
• EDATE: Adds months to a date
• EOMONTH: Returns last day of month

Date Serial Number System

Excel counts days from January 1, 1900 (day 1) to December 31, 9999 (day 2,958,465).

Example: January 1, 2023 = 44927

The DATEDIF Function Explained

The DATEDIF function (Date + Difference) calculates the difference between two dates in years, months, or days. Its syntax is:

=DATEDIF(start_date, end_date, unit)

Unit Argument	Returns	Example
“y”	Complete years between dates	=DATEDIF(“1/1/2020″,”1/1/2023″,”y”) → 3
“m”	Complete months between dates	=DATEDIF(“1/1/2023″,”6/15/2023″,”m”) → 5
“d”	Days between dates	=DATEDIF(“1/1/2023″,”1/15/2023″,”d”) → 14
“ym”	Months between dates after complete years	=DATEDIF(“1/1/2020″,”6/15/2023″,”ym”) → 5
“yd”	Days between dates after complete years	=DATEDIF(“1/1/2020″,”6/15/2023″,”yd”) → 166
“md”	Days between dates after complete months/years	=DATEDIF(“1/1/2023″,”6/15/2023″,”md”) → 14

Important Notes About DATEDIF

• Not listed in Excel’s function library (must be typed manually)
• Returns #NUM! error if start_date > end_date
• Behavior changed in Excel 2013+ for “md” unit
• Not available in Excel Online (as of 2023)

Alternative Methods for Calculating Months

Method 1: Using YEAR and MONTH Functions

For simple month calculations without DATEDIF:

= (YEAR(end_date)-YEAR(start_date))*12 + MONTH(end_date)-MONTH(start_date)

Example: = (YEAR(“6/15/2023”)-YEAR(“1/1/2020”))*12 + MONTH(“6/15/2023”)-MONTH(“1/1/2020”) → 41

Method 2: Using EDATE Function

The EDATE function adds months to a date, which can be used to count months between dates:

= MONTH(EDATE(start_date,count)-1) - MONTH(start_date-1)

Where “count” is a large number that ensures EDATE goes past the end date.

Method 3: Using DAYS360 Function

For financial calculations that use 30-day months:

= DAYS360(start_date, end_date)/30

Note: This gives approximate months based on 360-day years.

Method	Accuracy	Best For	Excel Version Support
DATEDIF	High	Precise month calculations	All (except Online)
YEAR/MONTH	Medium	Simple calculations	All
EDATE	High	Complex date manipulations	All
DAYS360	Low	Financial calculations	All
YEARFRAC*12	Medium	Fractional month calculations	All

Common Use Cases and Business Applications

1. Employee Tenure Calculations

HR departments frequently need to calculate:

• Years of service for benefits eligibility
• Months since last promotion for review cycles
• Time between performance evaluations

Example formula: =DATEDIF(hire_date,TODAY(),"m")

2. Contract and Subscription Management

Businesses track:

• Months remaining on service contracts
• Time between renewal periods
• Contract duration for billing cycles

Example: =DATEDIF(contract_start,contract_end,"m") & " months remaining"

3. Project Management Timelines

Project managers use month calculations for:

• Milestone tracking
• Gantt chart creation
• Resource allocation planning

Example: =DATEDIF(project_start,TODAY(),"m") & "/ " & DATEDIF(project_start,project_end,"m")

4. Financial Analysis

Financial professionals calculate:

• Loan durations in months
• Investment holding periods
• Amortization schedules

Example: =DATEDIF(loan_start,loan_end,"m")/12 & " years"

Advanced Techniques and Edge Cases

Handling Leap Years

Excel automatically accounts for leap years in date calculations. However, when calculating months between dates that span February 29:

• DATEDIF counts February as having 28 days in non-leap years
• For precise financial calculations, consider using DAYS360
• Test edge cases like dates around February 29, 2020 vs 2021

Partial Month Calculations

For prorated calculations (like partial month salaries):

= (YEARFRAC(start_date,end_date,1))*12

Where “1” uses actual days/actual days method (most accurate)

Negative Date Differences

To handle cases where end_date might be before start_date:

=IF(DATEDIF(start_date,end_date,"m")<0, "Future date", DATEDIF(start_date,end_date,"m"))

Array Formulas for Multiple Dates

For calculating months between multiple date pairs:

{=DATEDIF(range1,range2,"m")}

Enter with Ctrl+Shift+Enter in older Excel versions

Excel Version Differences and Compatibility

Different Excel versions handle date calculations slightly differently:

Excel Version	DATEDIF Behavior	YEARFRAC Default	Maximum Date
Excel 365/2021	Standard behavior	Basis 0 (US 30/360)	12/31/9999
Excel 2019	Standard behavior	Basis 0	12/31/9999
Excel 2016	"md" unit bug fixed	Basis 0	12/31/9999
Excel 2013	"md" unit returns negative for same month	Basis 0	12/31/9999
Excel 2010	Legacy behavior	Basis 0	12/31/9999
Excel 2007	Legacy behavior	Basis 0	12/31/9999
Excel Online	DATEDIF not available	Basis 0	12/31/9999

Workarounds for Excel Online

Since DATEDIF isn't available in Excel Online, use:

= (YEAR(end_date)-YEAR(start_date))*12 + MONTH(end_date)-MONTH(start_date) - IF(DAY(end_date)
    

Best Practices for Reliable Date Calculations

1. Always validate inputs: Use Data Validation to ensure cells contain valid dates
2. Document your formulas: Add comments explaining complex date calculations
3. Test edge cases: Verify behavior with:
   • Same start and end dates
   • Dates spanning month/year boundaries
   • Leap day (February 29)
   • Negative date differences
4. Consider time zones: If working with international dates, standardize on UTC
5. Use named ranges: For better readability in complex formulas
6. Create helper columns: Break down complex calculations into steps
7. Version control: Note which Excel version formulas were developed in

Performance Considerations

For workbooks with thousands of date calculations:

• Use Excel Tables for structured references
• Consider Power Query for large datasets
• Avoid volatile functions like TODAY() in large ranges
• Use manual calculation mode during development

Learning Resources and Further Reading

For more advanced Excel date calculations, consult these authoritative sources:

• Microsoft Official DATEDIF Documentation - The most current information straight from Microsoft
• Excel UserVoice - DATEDIF Feature Request - Community discussion about DATEDIF's official status
• Corporate Finance Institute - DATEDIF Guide - Financial applications of date functions
• GCFGlobal Excel Date Functions Tutorial - Beginner-friendly introduction to date calculations

Recommended Books

• "Excel 2023 Power Programming with VBA" by Michael Alexander
• "Advanced Excel Formulas" by Jordan Goldmeier
• "Excel Dashboards and Reports" by Michael Alexander
• "Financial Modeling in Excel For Dummies" by Danielle Stein Fairhurst

Frequently Asked Questions

Why doesn't DATEDIF appear in Excel's function list?

DATEDIF was included in early versions of Excel for Lotus 1-2-3 compatibility. Microsoft never removed it but also never officially documented it in the function library. It remains fully functional in all desktop versions of Excel.

How does Excel handle the year 1900 leap year bug?

Excel incorrectly treats 1900 as a leap year (February has 29 days) to maintain compatibility with Lotus 1-2-3. This only affects dates between March 1, 1900 and February 28, 1900. For all practical business purposes, this bug has no impact on modern date calculations.

Can I calculate business months (20 working days = 1 month)?

Yes, but you'll need a custom formula. First calculate the number of working days with NETWORKDAYS, then divide by your definition of a business month:

=NETWORKDAYS(start_date,end_date)/20

Adjust the divisor (20 in this example) to match your organization's definition of a business month.

How do I calculate months between dates excluding weekends?

Combine NETWORKDAYS with a conversion factor:

= (NETWORKDAYS(start_date,end_date)/5)*12/52

This approximates by converting working days to working months (assuming 5-day work weeks and 52-week years).

Why do I get different results between DATEDIF and manual calculations?

Common reasons include:

• Not accounting for the day of the month (DATEDIF is precise about month boundaries)
• Time components in your dates (use INT() to remove times)
• Different handling of the "md" unit in Excel 2013 vs 2016+
• Leap year differences in February calculations