This paper presents a new approach for calculating the crack growth under spectrum loading in various different industrial applications. The paper includes (1) An original model based on the crack closure concept. The model combines a cycle by cycle analysis with a conservative cycle counting method similar to the “rain flow” one. A rule that fixes the crack tip opening point at every cycle to take into account the R ratio effect and the retardation effects is developed. (2) A method used for the determination of parameters. The model requires only three parameters that can be obtained with two simple crack growth tests. These two tests give both the values of parameters and the K range where the model is valid. The three parameters depend on the material and the specimen thickness. (3) Some industrial applications—the results show a good correlation between tests and calculations for several different materials. Furthermore, calculation with standard fatigue spectra (TWIST, MINITWIST, FALSTAFF) are given for a range of parameters.