We predict the $\eta /{\pi }^0$ ratio at low $p_T$ ($p_T\lesssim 3GeV/c$) using the measured charged $K/\pi$ ratio and model input from a blast-wave framework with feeddown contributions. This approach can provide improved, data-constrained background estimates for direct-photon and dilepton measurements in heavy-ion collisions. In this approach, the explicit modeling of radial flow and hadronic feeddown enables an uncertainty estimate for the low-$p_T$ extrapolation of the $\eta /{\pi }^0$ ratio. Using central Pb–Pb collisions at $\sqrt{s_{NN}}=2.76$~TeV as an example, we find that the $\eta$-related decay-photon uncertainty at $p_T\approx 1GeV/c$ is of order 10% of the expected direct-photon signal.