This paper presents a new model for analyzing fission-track data from natural apatite samples, based on recent laboratory data on fission-track annealing in various apatites and an empirical correction for fission-track length anisotropy. The model uses revised statistical methods to evaluate how well empirical equations fit laboratory data and reproduce expected behavior over geological time scales. It is found that "fanning Arrhenius" models of mean track length are not the best for this data. Instead, fitting c-axis projected lengths with a model incorporating some curvature on an Arrhenius plot produces better agreement with geological benchmarks. The model can reproduce the laboratory-time-scale behavior of any two apatites with a simple one- or two-parameter equation. This function converts the reduced fission-track length of one apatite with a certain time-temperature history into the length that would be measured in a second, less-resistant apatite with the same history. This conversion allows a single model to encompass the annealing behavior of all studied apatites. The model's predictions closely match those from fits to data for individual apatites, suggesting that although the conversion equation is imperfect, it provides an excellent practical solution for characterizing the range of kinetic variability in apatite fission-track annealing. The paper discusses the variability of apatite fission-track annealing kinetics, emphasizing the importance of considering kinetic differences among apatites. It highlights the limitations of monokinetic models for studying natural samples with multikinetic apatite populations, which are common in sedimentary rocks and some igneous rocks. The paper also presents geological benchmarks for evaluating apatite annealing models, including high- and low-temperature benchmarks. High-temperature benchmarks are useful for determining when fission tracks fully anneal, while low-temperature benchmarks are important for interpreting track-length data correctly. The paper defines three index temperatures: closure temperature (Tc), total annealing temperature (TA), and 100% fission-track fading temperature (TF). These temperatures are used to describe annealing behavior in different situations. The paper also discusses the challenges of interpreting fission-track data, including the need for accurate down-hole temperatures, independent time-temperature paths, and kinetic indicators for all apatites studied. It presents results from the Otway Basin and other studies, showing that different apatites can exhibit significantly different annealing behaviors. The paper concludes that the new model provides a practical solution for characterizing the range of kinetic variability in apatite fission-track annealing.This paper presents a new model for analyzing fission-track data from natural apatite samples, based on recent laboratory data on fission-track annealing in various apatites and an empirical correction for fission-track length anisotropy. The model uses revised statistical methods to evaluate how well empirical equations fit laboratory data and reproduce expected behavior over geological time scales. It is found that "fanning Arrhenius" models of mean track length are not the best for this data. Instead, fitting c-axis projected lengths with a model incorporating some curvature on an Arrhenius plot produces better agreement with geological benchmarks. The model can reproduce the laboratory-time-scale behavior of any two apatites with a simple one- or two-parameter equation. This function converts the reduced fission-track length of one apatite with a certain time-temperature history into the length that would be measured in a second, less-resistant apatite with the same history. This conversion allows a single model to encompass the annealing behavior of all studied apatites. The model's predictions closely match those from fits to data for individual apatites, suggesting that although the conversion equation is imperfect, it provides an excellent practical solution for characterizing the range of kinetic variability in apatite fission-track annealing. The paper discusses the variability of apatite fission-track annealing kinetics, emphasizing the importance of considering kinetic differences among apatites. It highlights the limitations of monokinetic models for studying natural samples with multikinetic apatite populations, which are common in sedimentary rocks and some igneous rocks. The paper also presents geological benchmarks for evaluating apatite annealing models, including high- and low-temperature benchmarks. High-temperature benchmarks are useful for determining when fission tracks fully anneal, while low-temperature benchmarks are important for interpreting track-length data correctly. The paper defines three index temperatures: closure temperature (Tc), total annealing temperature (TA), and 100% fission-track fading temperature (TF). These temperatures are used to describe annealing behavior in different situations. The paper also discusses the challenges of interpreting fission-track data, including the need for accurate down-hole temperatures, independent time-temperature paths, and kinetic indicators for all apatites studied. It presents results from the Otway Basin and other studies, showing that different apatites can exhibit significantly different annealing behaviors. The paper concludes that the new model provides a practical solution for characterizing the range of kinetic variability in apatite fission-track annealing.