CALCULATE Function
Evaluates an expression in a context that is modified by the specified filters.
Term 
Definition 

expression 
The expression to be evaluated. 
filter1 , filter2 ,… 
(optional) A comma separated list of Boolean expression or a table expression that defines a filter. 
The expression used as the first parameter is essentially the same as a measure.
The following restrictions apply to Boolean expressions that are used as arguments:

The expression cannot reference a measure.

The expression cannot use a nested CALCULATE function.

The expression cannot use any function that scans a table or returns a table, including aggregation functions.
However, a Boolean expression can use any function that looks up a single value, or that calculate a scalar value.
If the data has been filtered, the CALCULATE function changes the context in which the data is filtered, and evaluates the expression in the new context that you specify. For each column used in a filter argument, any existing filters on that column are removed, and the filter used in the filter argument is applied instead.
To calculate the ratio of current reseller sales to all reseller sales, you add to the PivotTable a measure that calculates the sum of sales for the current cell (the numerator), and then divides that sum by the total sales for all resellers (the denominator). To ensure that the denominator remains the same regardless of how the PivotTable might be filtering or grouping the data, the part of the formula that represents the denominator must use the ALL function to clear any filters and create the correct total.
The following table shows the results when the new measure, named All Reseller Sales Ratio, is created by using the formula in the code section.
To see how this works, add the field, CalendarYear, to the Row Labels area of the PivotTable, and add the field, ProductCategoryName, to the Column Labels area. Then add the new measure to the Values area of the PivotTable. To display the numbers as percentages, apply percentage number formatting to the area of the PivotTable that contains the new measure, All Reseller Sales Ratio.
All Reseller Sales 
Column Labels 





Row Labels 
Accessories 
Bikes 
Clothing 
Components 
Grand Total 
2005 
0.02% 
9.10% 
0.04% 
0.75% 
9.91% 
2006 
0.11% 
24.71% 
0.60% 
4.48% 
29.90% 
2007 
0.36% 
31.71% 
1.07% 
6.79% 
39.93% 
2008 
0.20% 
16.95% 
0.48% 
2.63% 
20.26% 
Grand Total 
0.70% 
82.47% 
2.18% 
14.65% 
100.00% 
=( SUM('ResellerSales_USD'[SalesAmount_USD])) /CALCULATE( SUM('ResellerSales_USD'[SalesAmount_USD]) ,ALL('ResellerSales_USD'))
The CALCULATE expression in the denominator enables the sum expression to include all rows in the calculation. This overrides the implicit filters for CalendarYear and ProductCategoryName that exist for the numerator part of the expression.