**SUM and the =OFFSET function**

Sometimes it is necessary to base a calculation on a set of cells in different locations.

An example would be when a total is required from certain months of the year, such as

the last 3 months in relation to the current date.

One solution would be to retype the calculation each time new data is entered, but this

would be time consuming and open to human error.

A better way is to indicate the start and end point of the range to be calculated by

using the =OFFSET() function.

The =OFFSET() picks out a cell a certain number of cells away from another cell.

By giving the =OFFSET() the address of the first cell in the range which needs to

be totalled, we can then indicate how far away the end cell should be and the =OFFSET()

will give us the address of cell which will be the end of the range to be totalled.

The =OFFSET() needs to know three things;

1. A cell address to use as the fixed point from where it should base the offset.

2. How many rows it should look up or down from the starting point.

3. How many columns it should look left or right from the starting point.

results in the range being summed as E24:E24.

This example uses E29 as the starting point and offsets 1 col to pick out

cell F29 resulting in a the range E29:F29 being summed.

=SUM(E34:OFFSET(E34,0,2))

This example uses E34 as the starting point and offsets 2 cols to pick out

cell G34 resulting in a the range E34:G34 being summed.

**Using =OFFSET() Twice In A Formula**

which needs to be totalled.

=SUM(OFFSET(E45,0,1):OFFSET(E45,0,1))

The cell E45 has been used as the starting point for both offsets and each has

been offset by just 1 column. The result is that just cell F45 is used as the

range F45:F45 for the sum function to calculate.

=SUM(OFFSET(E51,0,1):OFFSET(E51,0,2))

The cell E51 has been used as the starting point of both offsets, the first offset is

offset by 1 column, the second by 2 columns. The result is the range F51:G51 which

is then totalled.

=SUM(OFFSET(E57,0,1):OFFSET(E57,0,3))

The cell E57 has been used as the starting point for both offsets, the first offset is

offset by 1 column, the second by 3 columns. The result is the range F57:H57 which

is then totalled.

**Example**

To calculate the total of a specific group of months the =OFFSET() function has been used.

The Start and End dates entered in cells F71 and F72 are used as the offset to produce

a range which can be totalled.

** Explanation**

The formula displayed below are only dummies, but they will update as you enter

dates into cells F71 and F72.

**Formula 1 =SUM( OFFSET(D79,0,MONTH(F71)) : OFFSET(D79,0,MONTH(F72)) ) **

This is the actual formula entered by the user.

**Formula 2 =SUM( OFFSET(D79,0,MONTH(2)) : OFFSET(D79,0,MONTH(3)) )
**This shows how the =MONTH function calculates the month number.

In this example the values of the months are 2 and 3 for Feb and Mar.

These values are the ‘offsets’ relative to cell D79.

**Formula 3 =SUM( OFFSET(D79,0,2) : OFFSET(D79,0,3) )
**This shows where the month numbers are used in the =OFFSET function.

**Formula 4 =SUM( F79:G79 )
**This shows how the =OFFSET eventually equates to cell addresses

to be used as a range for the =SUM function.

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