While the primary goal for first-time marathon runners is just to reach the finish line, most second-timers (and beyond) aim for something more—to beat their first marathon time. But what should you target? One way to determine a realistic new marathon time goal is to base it on your performance in a 5-K, 10-K, or half-marathon tune-up race; plug your time into a prediction calculator to see what your marathon time could be. This is no guarantee, but it could be one helpful guideline to use in the goal-setting process.