Developed by NYU professor Edward Altman in 1968, the Z-Score was originally designed to predict corporate bankruptcy within 2 years. It combines five weighted financial ratios into a single number. A score above 2.99 indicates the 'Safe Zone' (low distress risk). Between 1.81 and 2.99 is the 'Grey Zone' (uncertain). Below 1.81 is the 'Distress Zone' (elevated bankruptcy risk).
The model has proven remarkably durable. Original research showed 72% accuracy in predicting bankruptcies. However, it was calibrated on manufacturing companies from the 1960s and is today applied more broadly — including to contexts it was never designed for.
The same caveat applies here as with the Piotroski score: large-cap technology and software companies often score poorly on the Altman Z-Score not because they are actually distressed, but because their financial structures (high intangibles, capital-light models, aggressive buybacks) make traditional accounting ratios appear abnormal. A company like Microsoft or Apple with hundreds of billions in cash and government-bond-level credit ratings may score in the 'Grey Zone' simply because their retained earnings approach is different.
Use the Z-Score as a directional signal for traditional businesses, and always pair it with market cap, cash position, and credit ratings for software or platform companies.