To predict fatigue crack initiation life under variable loading easily, an expert system is developed, which is easy for ordinary engineering designers to use and can be also effectively utilized by fatigue researchers of any level, for discussing and evaluating various estimation methods associated with fatigue life prediction. The expert system is developed using a commercial expert system shell, Acquire. A concept of generalized modification of S-N curve including most of principal damage rules proposed so far is introduced to consider the load interaction effect under variable loading and used as the default damage rule in the expert system. The performance of the expert system is tested using the fatigue life data of the SAE Test Program on two steels. The expert system shows very good performance, providing moderate conservative predictions. (C) 2008 Elsevier Ltd. All rights reserved.