DOB (Age from Date of Birth)

Always Use DATEDIF for Age in Years

DATEDIF is the most accurate method for calculating complete years of age. Unlike simple arithmetic (TODAY()-DOB)/365, DATEDIF correctly handles leap years and varying month lengths. It returns exactly the number of birthdays a person has had, which is the legal and commonly accepted definition of age.

Combine Multiple DATEDIF for Exact Age

For precise age breakdowns in years, months, and days, chain three DATEDIF functions with different unit parameters. Use "Y" for complete years, "YM" for remaining months after years, and "MD" for remaining days after months. This provides exact age calculations essential for pediatric medicine and legal applications.

Use IF to Hide Zero Values

When displaying age in years and months, zero values look unprofessional ("0 Years, 3 Months"). Wrap each DATEDIF component in an IF statement to hide zeros: IF(DATEDIF(...)=0,"",DATEDIF(...)&" Years, "). This creates cleaner displays like "3 Months" instead of "0 Years, 3 Months" for infants.

Implement Comprehensive Error Handling

Production spreadsheets must handle edge cases: blank cells, future dates, text entries, and invalid dates. Use IFERROR as outer wrapper, then IF(ISBLANK()) to check for empty cells, and IF(DOB>TODAY()) to catch future dates. This prevents error messages from appearing and guides users to correct data entry.

Avoid Simple Arithmetic Division

Never use formulas like (TODAY()-DOB)/365 or /365.25 for age calculations. These methods don't account for actual calendar dates and will produce incorrect results. For someone born on Feb 29, these formulas give wrong ages in non-leap years. Always use DATEDIF or YEARFRAC for accurate date calculations.

Use YEARFRAC for Decimal Ages

When you need fractional years (e.g., 25.5 years for actuarial calculations), use YEARFRAC with basis 1 (actual/actual). Wrap in ROUNDDOWN to control decimal places: ROUNDDOWN(YEARFRAC(DOB,TODAY(),1),2). This provides precise age including fractions, useful for insurance premiums and financial planning.

Calculate Age at Specific Date

Replace TODAY() with any date reference to calculate age as of that date. This is crucial for historical records, retirement calculations at specific retirement date, or determining age at hire. Use: DATEDIF(birth_date, specific_date_cell, "Y"). Perfect for "age at hire", "age at retirement", or "age on policy start date".

Format DOB Columns as Date Format

Before entering birth dates, format the entire column as Date format (Ctrl+1 > Date). This prevents Excel from misinterpreting entries. When dates are formatted as text (common when copying from other sources), DATEDIF returns #VALUE! error. Use TEXT() or DATEVALUE() functions to convert text dates before calculation.

DATEDIF Won't Appear in Autocomplete

DATEDIF is an undocumented legacy function in Excel, so it won't show up in function autocomplete or help files. However, it works perfectly in both Excel (all versions) and Google Sheets. Type it manually: =DATEDIF( and Excel will recognize it. Consider creating a formula template or using cell comments to document the formula for other users.

Add Data Validation to Prevent Future Dates

Prevent user errors by setting data validation on DOB columns. Set validation criteria to: Date less than or equal to =TODAY(). This stops users from accidentally entering future dates. Add a custom error message: "Birth date cannot be in the future." This proactive approach eliminates the #NUM! error before it occurs.

Use Conditional Formatting to Highlight Anomalies

Set up conditional formatting to automatically flag suspicious ages: color cells red if age > 100 years or < 0 years. Use formula: =OR(DATEDIF($A2,TODAY(),"Y")>100, DATEDIF($A2,TODAY(),"Y")<0). This visual system catches data entry errors immediately, such as typos in year (1924 vs 2024) or impossible dates.

Consider Regional Date Format Differences

Excel interprets dates differently based on regional settings: US uses MM/DD/YYYY, most other regions use DD/MM/YYYY. When sharing files internationally, use unambiguous date formats like 15-Jan-1990 or enter dates with DATE(year, month, day) function: DATE(1990, 1, 15). This prevents misinterpretation when 01/05/1990 could mean Jan 5 or May 1.