In my experience that's where story points come in. "This comparable project took this number of story points, therefore <new project> should be similar, result

In my experience that's where story points come in. "This comparable project took this number of story points, therefore <new project> should be similar, resulting in a comparable amount of time." The usage of story points help to adjust for complexity. The story points are that data point in the past used to indicate the future.