Ancient magnetic field intensity estimates from rocks, can provide information about the early habitability of the Earth and formation of the Solar System. Ancient magnetic field intensities are recovered from rocks, by replicating the magnetic remanence acquisition process which occurs in nature in the laboratory. In nature, this magnetic remanence is acquired by cooling rocks from above their magnetic ordering temperature (∼600°C) to ambient temperature, in a weak magnetic field (a thermoremanence). Thermoremanences can be stable over billions of years. The intensity of thermoremanence is affected by the rate at which rocks cool. In the laboratory, cooling times are of the order of 1 hr, but in nature for intrusive rocks, the cooling time can be millions of years. It is necessary to make a cooling-rate correction. Previously this was done by multiplying ancient magnetic field intensity estimates by a factor derived from extrapolations of laboratory findings on other rocks. In this publication, we describe a new method and accompanying software that provides a unique cooling-rate correction based on a sample’s magnetic properties. That is, the cooling-rate correction is tailored to the rocks themselves, and is not based on a calibration factor. The software is available on GitHub.