The number of neutrons in an atom of iron is variable, with the most common number being 30. While the number of protons is diagnostic of an atom and does not change without changing the element itself, the number of neutrons varies by isotope.
Iron has four stable isotopes, with iron 56 being the most abundant. This isotope represents almost 92 percent of the iron found in nature, and its atoms contain 30 neutrons. Other stable isotopes of iron can have 29, 31 or 32 neutrons. Iron 74, by contrast, has 48 neutrons and decays in just over 638 nanoseconds.