Usually, it is considered bad practice to store calculated values. This should be done via a form.
If you edit a single value, the calculated result is likely to be wrong. It would be pointless to design a method of dealing with this when the right thing to do is to avoid the situation altogether. I agree that a Totals query would be the way to go IF a form is not involved. If it is, I'd do the calculation in the form itself.
If the displayed table field names are not captions, you are not following recommended naming practices either, which at best causes extra typing and care to avoid issues; at the worst, non-functioning procedures or methods with or without error messages.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.