The bolometric luminosity (Lbol) of active galactic nuclei (AGNs) is a key tracer of accretion physics, but its direct determination is often hindered by limited spectral coverage and contamination of the host galaxy. Bolometric corrections (κλ = Lbol/Lλ) offer a practical means of estimating Lbol, with the X-ray bolometric correction (κ2−10) being crucial for exploring the coupling between the accretion disk and the X-ray corona. Here we present multiepoch, multiwavelength observations of five highly variable, changing-state AGNs that span more than 3 orders of magnitude in Eddington ratio ( (Formula presented) −3.6≲logλEdd≲−0.5 ). This unique dataset reveals a remarkably tight relation between κ2−10 and λEdd, with an intrinsic scatter of only ∼0.05 dex. We find that while the sources show bolometric corrections following different tracks in luminosity space that depend on black hole mass, they all display the same κ2−10-λEdd trend. This shows unambiguously that λEdd is the primary driver of X-ray bolometric corrections and points to a tight underlying trend that can be used to obtain reliable estimates of bolometric output from X-ray luminosities. Our results highlight how time-domain, multiwavelength observations of variable AGN offer unique insights into the accretion flow structure and its radiative output.