Abstract: A gage for measuring accumulated fatigue damage, or accumulated strain experience, and remaining fatigue life in a structure subjected to repeated loadings in relation to predictions or calibration tests. The disclosed embodiment has a thin, nominally rectangular metal base of uniform thickness which has a very narrow crack-like slit cut in one side and a teflon parting strip attached to the base underlying the slit. When the gage is attached to a structure with a suitable adhesive and the structure is subjected to repeated loading, a fatigue crack immediately begins at the inner end of the slit and increases in length as an approximately linear function of the accumulative fatigue damage strains incurred by the structure. The crack in the gage occurs in advance of and independently of any crack in the structure itself.