The IF function You can use the IF function to make Excel select from a pair of possible outputs based on whether the inputs to the function meet your specified criterion or not. For instance, you might take a range of temperature measurements over several days. Having recorded this data in a spreadsheet, you could then use an IF function to ask Excel to decide whether a day should be called ‘hot’ or ‘cold’ depending on the temperatures you have recorded. Parameters for the IF function Parameters are things that a function needs in order to return a valid answer. The IF function has three parameters:    The logical test: this is a question that the IF function asks of a piece of data – it must have a yes/no answer The true response: this is what will happen if the IF function gets a ‘yes’ answer to the logical test The false response: this is what will happen if the IF function gets a ‘no’ answer These parameters are entered in brackets, separated by commas. They must be entered in the above order or Excel will not understand the function. Constructing an IF function Using the example of determining whether a day was ‘hot’ or ‘cold’ depending on the temperature measured in that day, we can construct an IF function so that Excel can test each piece of data. We can put an IF function in column C to test the data in the cells of column B to decide whether the weather is hot or cold. A day will be considered hot if the temperature exceeds 25°C. This cell will display ‘hot’ if the temperature entered in cell B3 is over 25°C and ‘cold’ if it is below that temperature The logical test used in this example is B2>25 – Excel uses this to ask the question “is the value in cell B2 more than 25?” If the answer to this question is “Yes, it’s more than 25”, then the cell will say ‘hot’ – this is the true response. If the value is “No, it is not more than 25”, the cell will return the false response, and say ‘cold’. To return a word as the answer to your question, you must put speech marks around the word or it will not display properly. The logical test asks if the value in B2 is more than 25 If the answer is yes, the cell will say hot If the answer is no, the cell will say cold =IF(B2>25,″hot″,″cold″) Parameters are separated by commas Speech marks indicate that the result will be text rather than a number For this cell, the IF function has returned cold, because the temperature in cell B2 is below 25°C We can then use auto fill to add this function to the other cells in column C. The reference in the function is a relative cell reference, so it always refers to the cell immediately to the left of the function rather than always referring to cell B2. This means that each calculation we auto fill will be unique for the temperature value in each row. For this cell, the IF function has returned hot, because the temperature in cell B8 is above 25°C Logical tests The logical tests used in IF functions are usually constructed using comparison operators. These compare two values and give a yes or no answer depending on the result of the comparison. This table shows the comparison operators you can use to construct a logical test in Excel: Test Operator Equals = Not equal to <> Greater than > Less than < Greater than or equal to >= Less than or equal to <= You can use these to compare the value in a cell to an absolute value or to a value from another cell. In the example above, we have used an absolute value, comparing the cell contents to see if they are greater or less than 25. We could use a relative value to compare the cells to one another; for instance instead of deciding whether a day was hot or cold, we could have asked whether it was warmer or colder than the day before. An example function for this would be: =IF(C2>B2,″warmer″,″colder″) Returning the result of a calculation You can build an IF function that returns the result of a calculation rather than an absolute value. To return the result of a calculation, you can put calculations rather than values or text into the true and false responses. For example, if we have purchased some stationery and there is a sales tax of 15% that only applies to items costing over £1, we can set up an IF function which will calculate the amount of tax payable on each item. We would like this cell to display a tax of 15% if the item in this row costs more than £1, and zero otherwise The IF function to calculate this would be: The logical test asks if the value in B2 is more than 1 If the condition in the logical test is met, the tax will be calculated for that item =IF(B2>1,B2*0.15,0) If the condition is not met, the cell will display zero Here we have set a condition that the cost of the item be more than £1, and said that if it is, we will calculate 15% of the cost of the item by multiplying the cost by 0.15. If the condition is not met, we will return zero instead. Auto filling for the rest of the column returns the tax value for each of the items, and zero where there is no tax charged Nesting IF functions A nested IF function is one which is used within another IF function in place of one of the responses. You may find that you need to pose more than one question before you determine which output you would like to produce. To do this, you can use a nested set of IF functions to refine the results of the logical test to give a more accurate answer. This means that you can use a series of yes/no questions to ask questions which have more sophisticated answers. To return to our earlier example, we have said that days where the temperature is over 25°C are hot, and those below that temperature are cold. We could refine that to say that days over 25°C are hot, those below 10°C are cold, and anything in between we will consider to be warm. To achieve this, we need to ask two yes/no questions before we can give an answer:   Is the temperature above 25°C? Is the temperature below 10°C? The function we will use to do this is: A second IF function is used in place of the false response – it is nested within the first IF function =IF(B2>25,″hot″,IF(B2<10,″cold″,″warm″)) The results for the nested function will determine what will happen if the condition is not met for the first logical test Excel will colour code both the cell references and the brackets for nested functions to make it easier to complete all your functions. Excel uses colour coding for both brackets and cell references for nested functions Using nested functions, we can return three different responses using yes/no questions You can nest up to 64 IF functions within Excel 2010 to build highly refined results.