Discussed below is how to control when a formula calculates.
The calculation mode of a workbook controls whether its formulas calculate automatically or manually when cell values are changed.
Microsoft Excel has the capability for a user to control its workbook calculation mode. A user will set this mode to manual disabling all calculations when a workbook takes a long time to calculate when new values are entered. Generally this time lag occurs when you have thousands of complex formulas in a workbook. To set the calculation mode to manual, proceed to the Ribbon, select the Formulas tab and then find the Calculation grouping on the tab. Click on the Calculation Options button and select you guessed it Manual. This process is pictured to the below.
Once manual is engaged, Excel will only recalculate when you tell it to. You can recalculate by pressing the F9 key or you can click the Calculate button in the status bar at the bottom left-hand corner of the Excel screen. Note that Shift+F9 can be pressed to only calculate the sheet that you are on. By the way, looking for this button when a workbook first opens or is being used is a great way to know instantly if the calculation mode has been set to manual. Note that if the workbook has a circular reference, bad idea, then this button will also be present. Also if you set the mode to manual and you save your workbook, that setting will be stored with the workbook so when the file is reopened, it will reengage. Be careful because many Excel users are not used to seeing the calculation mode disabled and freak out when first encountering it. To turn it back on, select Automatic from the Calculation Options button.