Let $(M,g(\tau))$ be a complete backward Ricci flow on $\tau\in(0,t_0]$ with bounded curvature on compact subintervals, based at a regular point $(p,0)$. Let $\ell$ be Perelman's reduced distance from $(p,0)$ and let $\widetilde V(\tau)=\int_M (4\pi\tau)^{-n/2}e^{-\ell(q,\tau)}\,d\mu_\tau(q)$ whenever this integral is finite. If the pointed parabolic rescalings at $(p,0)$ converge locally smoothly to Euclidean space as $\tau\downarrow 0$, then $\widetilde V(\tau)$ is nonincreasing in $\tau$. Moreover,

\begin{align*} 0<\widetilde V(\tau)\le 1 \end{align*}

for every $\tau\in(0,t_0]$ for which the integral is finite.