TDFCalc is an application which implements a form of the linear-quadratic (LQ) equation suitable for comparing the biologically effective dose (BED) of external beam radiation therapy (EBRT) fractionation regimens. It calculates BED for a given alpha/beta ratio as a function of the dose per fraction and the number of fractions. It also calculates dose per fraction as a function of the number of fractions for a given BED. This enables very quick comparison of a modified fractionation regimen (e.g. hypofractionation) vs a conventional regimen.