V out = A d ( V in + − V in − ) + A c ( V in + + V in − 2 ) {\displaystyle V_{\text{out}}=A_{\text{d}}(V_{\text{in}}^{+}-V_{\text{in}}^{-})+A_{\text{c}}\left({\frac {V_{\text{in}}^{+}+V_{\text{in}}^{-}}{2}}\right)} A c {\displaystyle A_{\text{c}}} is called the common-mode gain of the amplifier.
V out = A d ( V in + − V in − ) + A c ( V in + + V in − 2 ) {\displaystyle V_{\text{out}}=A_{\text{d}}(V_{\text{in}}^{+}-V_{\text{in}}^{-})+A_{\text{c}}\left({\frac {V_{\text{in}}^{+}+V_{\text{in}}^{-}}{2}}\right)} A c {\displaystyle A_{\text{c}}} er kaldet common-mode forstærkningen af forstærkeren.