C_avg is the average concentration of a drug in the central circulation during a dosing interval in steady state. It is calculated by

${\displaystyle C_{\text{avg}}={\frac {AUC_{\tau ,{\text{ss}}}}{\tau }}}$

where ${\displaystyle AUC_{\tau ,{\text{ss}}}}$ is the area under the curve and ${\displaystyle \tau }$ the dosing interval.