On my form I have a sub-total field. I simply want the sub-total form to sum all the price extended fields for each product. I have tried the formula me.subtotal=me.field1+me.field2, etc.
But no total is appearing in the sub total field. Thanks in advance for any help someone might be able to provide.

Put the following in the Form Current event proc.
me.subtotal=me.field1+me.field2
In the after update event of fields 1,2,etc put Form_Current
HTH

I did what you had suggested, but the subtotal is reading the numbers together, rather then adding them together (eg. 141516, when it should read 45)

Also, I have 10 fields that would be added to get a sub-total. Many times less then 10 fields will be filled in. I would like the sub-total to read the total as the different fields are entered in (eg. 1st field is entered as 20, then the sub-total reads 20, 2nd field is entered as 30, then the sub-total changes to 50, etc.).

Thanks in advance for any help you might be able to provide

For some reason, Access is interpreting the values as text and concatenating them rather than adding them. Try using the Val() function.

me.subtotal = val(me.field1) + val(me.field2) + ....

As Rich suggested, the above statement goes in the Current event of the form. Since you want a running total, you'll need to execute the code in the AfterUpdate event of each of the fields. To do that, you can call the form's current event -

Call Form_Current