Master the FACTDOUBLE Function: Double Factorial Calculations in Excel
=FACTDOUBLE(number)The FACTDOUBLE function is a specialized mathematical tool in Excel that calculates the double factorial of a number, represented by the notation n!!. Unlike the standard factorial that multiplies all positive integers down to one, the double factorial multiplies only the odd or even numbers in a sequence, depending on whether the input is odd or even. This function proves invaluable in advanced statistical analysis, combinatorics, and scientific calculations where you need to compute products of alternating number sequences. Understanding FACTDOUBLE is essential for professionals working with complex mathematical models, probability distributions, and engineering calculations. Whether you're analyzing data patterns, creating statistical models, or solving combinatorial problems, this intermediate-level function provides a efficient solution without requiring nested formulas or array operations. Available across all modern Excel versions from 2007 through 365, FACTDOUBLE integrates seamlessly into your existing spreadsheet workflows and complements other mathematical functions like FACT, COMBIN, and PRODUCT.
Syntax & Parameters
The FACTDOUBLE function follows a straightforward syntax: =FACTDOUBLE(number), where 'number' is the only required parameter. This parameter must be a positive integer representing the value for which you want to calculate the double factorial. The function accepts values from 0 to 170, with 0 and 1 both returning 1 by definition. When you input an even number, FACTDOUBLE multiplies all even positive integers up to that number. For example, FACTDOUBLE(6) calculates 6 × 4 × 2 = 48. Conversely, with an odd number, it multiplies all odd positive integers up to that number; FACTDOUBLE(7) equals 7 × 5 × 3 × 1 = 105. The function automatically returns an error if you provide negative numbers, decimals, or non-numeric values. Understanding this behavior is critical because many users mistakenly assume FACTDOUBLE works like nested factorial operations. Always ensure your input is a whole number between 0 and 170 to avoid unexpected errors and ensure accurate calculations in your financial models or statistical analyses.
numberPractical Examples
Product Launch Timeline Analysis
=FACTDOUBLE(8)This formula calculates the double factorial of 8, which multiplies all even numbers: 8 × 6 × 4 × 2. This result represents possible arrangement patterns for tasks with alternating priority sequences in project scheduling.
Statistical Distribution Modeling
=FACTDOUBLE(9)/FACTDOUBLE(6)This formula divides the double factorial of 9 (9 × 7 × 5 × 3 × 1 = 945) by the double factorial of 6 (6 × 4 × 2 = 48), yielding 19.6875. This ratio is commonly used in statistical coefficients and probability calculations.
Engineering Combinatorics Calculation
=FACTDOUBLE(10)*FACTDOUBLE(5)This formula multiplies the double factorial of 10 (10 × 8 × 6 × 4 × 2 = 3,840) by the double factorial of 5 (5 × 3 × 1 = 15), resulting in 57,600. This represents combined permutation scenarios in complex engineering problems.
Key Takeaways
- FACTDOUBLE calculates double factorials by multiplying alternating number sequences—even or odd integers depending on input parity
- The function accepts only whole numbers from 0 to 170; inputs outside this range return #NUM! errors
- FACTDOUBLE is essential for statistical modeling, probability calculations, and advanced combinatorics without complex nested formulas
- Results grow exponentially; FACTDOUBLE(170) produces extremely large numbers requiring careful handling in spreadsheets
- Combine FACTDOUBLE with other functions like IF, MOD, and IFERROR to create robust, adaptive formulas for complex calculations
Pro Tips
Use FACTDOUBLE in lookup tables for frequently needed double factorial values. Pre-calculate and store results in a reference table to improve spreadsheet performance when the same calculations repeat across multiple formulas.
Impact : Reduces recalculation overhead and speeds up spreadsheet recalculation cycles, especially beneficial in large models with thousands of formulas.
Combine FACTDOUBLE with IFERROR to handle edge cases gracefully. Use =IFERROR(FACTDOUBLE(A1),"Invalid input") to provide user-friendly error messages instead of cryptic error codes.
Impact : Improves spreadsheet usability and prevents confusion when invalid data is encountered, making your models more robust and professional.
Remember that FACTDOUBLE results grow exponentially. FACTDOUBLE(170) produces a number with 306 digits. Use scientific notation or split calculations across multiple cells when working with large inputs to maintain readability.
Impact : Prevents display issues and makes large calculations more manageable and interpretable within your spreadsheet layout.
Test FACTDOUBLE formulas with small known values first before deploying in production models. Verify results manually: FACTDOUBLE(4) should equal 8 (4×2), and FACTDOUBLE(5) should equal 15 (5×3×1).
Impact : Ensures formula accuracy and catches logic errors early before they propagate through larger calculations or reports.
Useful Combinations
Double Factorial Ratio for Distribution Coefficients
=FACTDOUBLE(A1)/FACTDOUBLE(B1)Combines two FACTDOUBLE functions to calculate ratios commonly needed in probability distributions and statistical models. This pattern is essential for Gaussian distribution coefficients and moment calculations.
Conditional Double Factorial with IF Logic
=IF(MOD(A1,2)=0,FACTDOUBLE(A1),FACTDOUBLE(A1)*2)Uses IF with MOD function to apply different calculations based on whether the input is even or odd. This enables adaptive formulas that adjust results based on number properties.
Double Factorial in Probability Calculations
=FACTDOUBLE(A1)/(FACTDOUBLE(B1)*FACTDOUBLE(C1))Combines multiple FACTDOUBLE functions with division to calculate complex probability coefficients. This pattern is frequently used in advanced statistical modeling and combinatorial probability problems.
Common Errors
Cause: The input parameter is not a valid number. This occurs when you pass text, special characters, or cell references containing non-numeric values to FACTDOUBLE.
Solution: Verify that your input is a positive integer. Use =FACTDOUBLE(VALUE(A1)) if your number is stored as text, or check that the referenced cell contains only numeric data without formatting issues.
Cause: The input number is negative, a decimal, or exceeds 170. FACTDOUBLE only accepts whole numbers from 0 to 170 due to computational limits.
Solution: Ensure your input is between 0 and 170. If using decimals, apply INT() or ROUND() functions first: =FACTDOUBLE(INT(A1)) to convert to whole numbers before calculation.
Cause: The function name is misspelled or your Excel version doesn't recognize FACTDOUBLE. Older Excel versions or regional settings might use different function names.
Solution: Verify correct spelling: FACTDOUBLE (not FACT_DOUBLE or FACTDBL). Check your Excel version—FACTDOUBLE is available in Excel 2007 and later. If using an older version, use FACT() function instead with manual adjustments.
Troubleshooting Checklist
- 1.Verify the input is a positive whole number between 0 and 170; check for negative values or decimals
- 2.Confirm the cell reference contains numeric data, not text-formatted numbers; use VALUE() function if needed
- 3.Check Excel version compatibility—FACTDOUBLE requires Excel 2007 or later; older versions require FACT() alternative
- 4.Ensure formula syntax is correct: =FACTDOUBLE(number) with proper parentheses and no extra spaces
- 5.Test with simple known values like FACTDOUBLE(4)=8 to isolate whether the error is in the formula logic or data
- 6.Verify cell formatting isn't hiding errors; check for hidden rows, columns, or conditional formatting affecting results
Edge Cases
Input value is 0
Behavior: FACTDOUBLE(0) returns 1 by mathematical definition, consistent with standard factorial notation
This is correct behavior and serves as the base case for recursive calculations
Input value is 1
Behavior: FACTDOUBLE(1) returns 1, representing the product of only the number 1 itself
Both FACTDOUBLE(0) and FACTDOUBLE(1) return 1, which is mathematically correct
Input exceeds 170 or is negative
Behavior: Returns #NUM! error because Excel cannot compute factorials beyond this limit due to numerical overflow
Solution: Reduce the input value to stay within 0-170 range, or restructure calculations to use ratios instead of absolute values
This limitation is inherent to Excel's numerical precision; FACTDOUBLE(171) will always fail
Limitations
- •FACTDOUBLE only accepts whole numbers from 0 to 170; any input outside this range produces an error, limiting its use in certain advanced statistical applications
- •Results grow exponentially, making FACTDOUBLE(170) produce numbers with 306 digits that exceed practical display and calculation capabilities in standard spreadsheet cells
- •The function cannot handle negative numbers, decimals, or text values directly; you must pre-process data with INT(), ROUND(), or VALUE() functions, adding complexity to formulas
- •FACTDOUBLE is unavailable in Excel versions prior to 2007; users of older versions must use alternative approaches combining FACT() with conditional logic or PRODUCT() functions
Alternatives
Compatibility
✓ Excel
Since 2007
=FACTDOUBLE(number) works identically across Excel 2007, 2010, 2013, 2016, 2019, and 365✓Google Sheets
=FACTDOUBLE(number) functions identically in Google SheetsGoogle Sheets supports FACTDOUBLE with identical syntax and behavior. Results are consistent across platforms.
✓LibreOffice
=FACTDOUBLE(number) is supported in LibreOffice Calc with equivalent functionality