Hi,
Your description is a bit vague but if i understand correctly, you can use a button to make the calculation. I havent included any logic to protect against empty fields.
form1.#subform[0].btnCalculate::click - (FormCalc, client)
grandTotal = subTotal + (subTotal * (salesTaxCbo / 100))
Assuming:
salesTaxCbo - Checkbox prefilled with tax percentage
subTotal - Numeric field
grandTotal - Numeric field which gets calculated amount.
btnCalculate - The button to calculate the grand total
![1311758_pastedImage_3.png 1311758_pastedImage_3.png](/t5/image/serverpage/image-id/6239i48423034E4BB0A16/image-size/large?v=v2&px=999)
----------------------------------------------------------
![1311745_pastedImage_2.png 1311745_pastedImage_2.png](/t5/image/serverpage/image-id/6240iFF385A9998A7339E/image-size/large?v=v2&px=999)
-----------------------------------------------------------
![1311759_pastedImage_4.png 1311759_pastedImage_4.png](/t5/image/serverpage/image-id/6241iFF5CB24116A36409/image-size/large?v=v2&px=999)