CAUTION: The Altman Z-Score is meant to be applied only to manufacturing firms that are near bankruptcy. It was not based on a sample including non-manufacturing firms (service firms, banks, etc.). Use it at your own risk with those companies, but beware that bankruptcy probabilities may be misstated.
The Altman Z-Score helps investors to gauge the probability of a company going bankrupt. Generally, firms with a score above 3.00 have a low probability of bankruptcy, and those with a Z-Score of less than 1.81 have a relatively high probability of bankruptcy.
Note that this is a probabilistic model, so it will not classify perfectly.
The score was first published in a 1968 paper by Edward Altman titled "Financial Ratios, Discriminant Analysis and the Prediction of Corporate Bankruptcy."
Altman re-tested the model in a 2000 paper titled "Predicting financial distress of companies: Revisiting the Z-score and Zeta models". The paper showed that the model still had utility for looking at manufacturers, though the number of misclassifications did increase over time.
Z = 1.2 x (Working Capital / Total Assets) + 1.4 x (Retained Earnings / Total Assets) + 3.3 x (Earnings Before Interest and Taxes / Total Assets) + 0.6 x (Market Value of Equity / Total Liabilities) + 1.0 x (Sales / Total Assets)
Working Capital = Current Assets - Current Liabilities
Market Value of Equity = Market Cap + Preferred Stock
YCharts calculates according to this formula.