You can use the following syntax to sum the values in every nth row in Google Sheets:

=sumif(ArrayFormula(mod((row(A1:A)-row(A1)+1),3)),0,A1:A)

This particular formula sums every **3rd** value in column A, starting at cell **A1**.

The following examples show how to use this syntax in practice with the following column of values in Google Sheets:

**Example 1: Sum Every Third Row**

We can use the following formula to sum the values in every third row (starting in cell **A1**) of column A:

=sumif(ArrayFormula(mod((row(A1:A)-row(A1)+1),3)),0,A1:A)

The following screenshot shows how to use this syntax in practice:

The sum of every third row turns out to be **37**.

We can manually verify this by taking the summation of every third row:

Sum: 15 + 10 + 3 + 9 = **37**.

**Example 2: Sum Every Sixth Row**

We can use the following formula to sum the values in every sixth row (starting in cell **A1**) of column A:

=sumif(ArrayFormula(mod((row(A1:A)-row(A1)+1),6)),0,A1:A)

The following screenshot shows how to use this syntax in practice:

The sum of every sixth row turns out to be **19**.

We can manually verify this by taking the summation of every sixth row:

Sum: 10 + 9 = **19**.

**Example 3: Sum Every Third Row Starting at Row 2**

We can use the following formula to sum the values in every third row (starting in cell **A2**) of column A:

=sumif(ArrayFormula(mod((row(A2:A)-row(A2)+1),3)),0,A2:A)

The following screenshot shows how to use this syntax in practice:

The sum of every third row (starting in cell **A2**) turns out to be **16**.

We can manually verify this by taking the summation of every third row, starting at cell **A2**:

Sum: 8 + 6 + 2 = **16**.

**Additional Resources**

The following tutorials explain how to perform other common tasks in Google Sheets:

Google Sheets: How to Multiply Column by a Constant

Google Sheets: How to Multiply Column by a Percentage

Google Sheets: How to Rank Items by Multiple Columns