[dragonwriter]

You're working class if you are renting your labor out to a capital owner to produce your income.

You're middle class if you are applying your own labor to capital you own to produce your income.

You're capitalist class if you are renting other people's labor to apply to capital you own to produce your income.

(These aren't discrete categories; they might be better read with "if you are" replaced with "to the extent you are".)