Thank you for your post.
The Bento to FileMaker Migration Tool will only transfer the values from the calculations and place them in Number fields. You can change this so it will calculate. I am happy to guide you through the process, but I'll need to know what fields are being calculated and what you are trying to accomplish. For instance, if the Bento calculation for a "Total Price" field was:
Subtotal + Tax
Then, in FileMaker Pro, pull down the File menu and select Manage -> Database...
Click on the Fields tab, find the "Total Price" field and click on it. Change the field type from Number to Calculation and click Change. In the Calculation dialog box, find the Subtotal field and double-click on it, enter a "+", and double-click the Tax field. Click OK.
If you feel uncomfortable performing these steps, feel free to send in your FileMaker file along with a Bento backup file, and I'll make the changes for you. I have sent you a private message with instructions where to send the files.