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We present a parameterized X‐ray solar flare effects model relating the physics of radiation transport to the observable impact of solar flares on low‐altitude ionospheric absorption of High Frequency (HF) signals. Tunable parameters of time‐varying flare spectral energy density and characteristic flare temperature provide a novel capability to simulate HF experiments over a wide range of X‐ray solar flare behavior. Results from our model are consistent with HF propagation data collected over a period of heightened solar flare activity during 5–7 September 2017, including M and X class solar flares. Our predictions and measurements are compared with results from D Region Absorption Prediction (Akmaev et al., 2010, https://www.ngdc.noaa.gov/stp/drap/DRAP-V-Report1.pdf) and the Wait Very Low Frequency (VLF)‐driven model (Wait & Spies,). Plain Language Summary: We present a physics‐based model for high‐frequency (HF) signal absorption resulting from the effects of X‐ray solar flares on the low‐altitude ionosphere. Our model calculates the extent of ionization enhancement in the D region due to an X‐ray flare and predicts the altitude‐dependent change of electron density and consequent increase in HF signal absorption. We demonstrate that results from our model are consistent with ionosonde data collected during three solar flare events. This model provides a novel approach to analyzing the impact of X‐ray solar flares on HF propagation and is complementary to the widely used empirical D Region Absorption Prediction and Wait models. Key Points: We developed a physics‐based model of HF absorption due to X‐ray solar flare impact on the low‐altitude ionosphereModel results are consistent with ionosonde data collected during flare events on a 3‐day experimental campaignThe model is a novel approach to X‐ray flare impact on HF propagation, complementing existing empirical models [ABSTRACT FROM AUTHOR]