I have been trying to add multiple fields together to come up with a result
for one field.
It seems to work with two fields, but when I add the third field (of 6 or
seven), It doesn't. Why?
Your subject line indicates you want this for an update query which
would save the calculated value in a table.
John Spencer indicated a possible reason why your query 'does not
work', (whatever that means).
However, even if it did work, calculated values should not be stored
in a table. Saving calculated data not only wastes space but can lead
to erroneous data if one of the components of the calculation has been
changed.
Any time you need the calculated result, re-calculate it, using John's
expression.