Answer

The formula to count duplicates in a column is COUNTIF. This function counts how many times a value appears within a specified range, which directly identifies duplicates when the count is greater than 1.

Primary Formula Using COUNTIF

The standard formula structure is shown below.

\text{COUNTIF(range, criteria)}

This formula evaluates each value against the range and returns the total number of occurrences.

Counting Duplicate Occurrences Per Row

To count how many times each value appears in a column, enter the following formula in an adjacent column.

\text{COUNTIF}(A:A, A2)

This formula counts how many times the value in cell A2 appears in column A.

Identifying Only Duplicate Values

A value is classified as a duplicate when the count returned by COUNTIF is greater than 1.

\text{COUNTIF}(A:A, A2) > 1

This logical evaluation returns TRUE for duplicate values and FALSE for unique values.

Counting the Total Number of Duplicate Values in a Column

To count how many duplicate entries exist in an entire column, excluding the first occurrence of each value, use the following formula.

\text{SUMPRODUCT}\left(\text{COUNTIF}(A:A, A:A)-1\right)

This formula aggregates duplicate counts and removes the initial unique instance of each value.

Counting Unique Values That Have Duplicates

To count how many distinct values appear more than once, use this formula.

\text{SUM}\left(--(\text{COUNTIF}(A:A, A:A)>1)\right)

This calculation returns the number of unique duplicated items rather than the total duplicate rows.

Windows and Mac Differences

There is no functional difference between the Windows and Mac versions of Excel for duplicate-counting formulas. The formulas operate identically across both platforms.

Important Accuracy Notes

1. Blank cells are counted unless excluded explicitly.

2. Text values are not case-sensitive by default.

3. Leading and trailing spaces are treated as distinct characters.

Credibility and Function Reliability

The COUNTIF function is a core Excel function documented in official Microsoft Excel support references. Its calculation logic remains stable across Excel versions and platforms.

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