org-table-formula-evaluate-inline

org-table-formula-evaluate-inline is a variable defined in `org-table.el'.
Its value is

t

Documentation:
Non-nil means TAB and RET evaluate a formula in current table field.
If the current field starts with an equal sign, it is assumed to be a formula
which should be evaluated as described in the manual and in the documentation
string of the command `org-table-eval-formula'. This feature requires the
Emacs calc package.
When this variable is nil, formula calculation is only available through
the command M-x org-table-eval-formula.

You can customize this variable.