I'm not sure what you mean by implement your own excel engine. The xamSpreadsheet works directly with our Excel Workbook class. Part of the functionality of that class is to perform calculations for the formulas in the Workbook. You can have the Workbook temporarily stop calculating by using the SuspendCalculations method (and then resume it with the ResumeCalculations). You can also set the CalculationMode to Manual to avoid having formulas update when the value of references the formula depends upon have changed (similar to the File->Options->Formulas->Calculation Options->Workbook Calculation setting in Excel). If you mean that you want to show the formulas in the cells similar to how Excel does when you show formulas in cells (e.g. either pressing ctrl+~ or checking File->Options->Advanced->Display options for this worksheet->Show formulas in cells) then you can set the DisplayOptions->ShowFormulasInCells to true for each Worksheet in your Workbook.