COMBINA in Excel: Count Repeated Selections and Check the Documented Scope

• Introduced: Microsoft marks the function as introduced in Excel 2013. Version-marker reference.
• Availability: official help lists Excel for Microsoft 365, Excel for Microsoft 365 for Mac, Excel 2024, Excel 2024 for Mac, Excel 2021, Excel 2021 for Mac, Excel 2019, Excel 2016.
• Checked: October 14, 2026; official COMBINA reference. Documentation and independently calculated examples; no native Excel execution or broader platform certification.

=COMBINA(number,number_chosen)

Both counts are required. Microsoft documents truncation of noninteger values and errors for nonnumeric or out-of-constraint inputs. Its current argument text also says the number of types must be at least the number selected.

That last restriction is narrower than the general mathematics of repetition, where a selection can contain more items than available types. This guide keeps its Excel worked controls within the published constraint and does not certify the native result of a number_chosen-greater-than-number call. Do not silently transfer a different program’s behavior into that gap.

Use three labels A, B and C and choose two units. With repetition the six groups are AA, AB, AC, BB, BC and CC:

=COMBINA(3,2)
=COMBIN(3,2)

Expected counts are 6 and 3. COMBIN excludes the three repeated-label groups. Both functions ignore internal order, so neither adds BA as an extra version of AB.

If a report instead distinguishes a first and second slot and permits repetition, there are 3×3=9 ordered outcomes. Write the order and repetition rules before choosing the formula.

Enter selected counts 1, 2, 3 and 4 in A2:A5. Fill =COMBINA(4,A2) down.

Expected counts are 4, 10, 20 and 35. More selected units create additional repeated mixtures, not additional distinct types. The third result agrees with the documented four-types/three-items model without borrowing the vendor’s example as the only check.

For a positive truncation control, =COMBINA(4.9,2.8) is expected to use 4 and 2 and return 10. Validate whole-number quantities in the source when the application requires indivisible units.

Distribute three indistinguishable tokens among four labeled boxes, with zero tokens allowed in a box and no upper capacity. A distribution is determined by four nonnegative counts summing to three.

=COMBINA(4,3)
=COMBIN(4+3-1,3)

Both mathematical expectations are 20. The second expression represents the stars-and-bars count: three token marks and three dividers determine a distribution across four boxes.

The boxes are labeled, so all tokens in box A differs from all tokens in box B. The tokens themselves are not labeled. If every box must receive at least one token, three tokens cannot fill four boxes, and this unrestricted formula would answer the wrong question.

Among the two-unit mixtures from four types A, B, C and D, count mixtures containing at least one A. All mixtures total 10; mixtures using only B, C and D total 6.

=COMBINA(4,2)-COMBINA(3,2)

Expected result: 4, corresponding to AA, AB, AC and AD. Subtraction works because the excluded cases are a subset of the same unrestricted outcome space.

The general positive-type mathematical formula is COMBIN(n+k−1,k). It does not resolve the narrower restriction printed in the current COMBINA argument description. The selected-count-greater-than-type-count behavior remains an explicit evidence hold here.

The examples avoid an all-zero configuration and negative fractional boundaries. Large outputs, exact native integer precision and all coercion details require separate validation rather than extrapolation from these small counts.

• Microsoft COMBINA reference.
• Editorial testing standards.

Worked inputs are fictional. Decimal answers are independently calculated mathematical expectations rounded to nine places, not captured native results. Extreme magnitudes, complete coercion matrices and cross-version numerical accuracy remain untested.