Of course, the time it takes to finish an Ironman will depend on your age. Here's the average time to finish an Ironman by age group.
But what if you're not average? What will your Ironman finish time be?
Two ways to arrive at the answer. First, if you've raced a half ironman, multiply that time by 2.1 for a ballpark estimate (see our Predicting Your Ironman Time Based on Your Half Ironman Time).
If you haven't completed a recent half ironman, your estimated bike split is the next best indicator, as it represents 50% of expected total finish time (see our 50% Rule), on average.
Planning on a 6 hour bike split? Then a 12 hour finish time is a realistic target, for example. Just make sure you don't go out too hard on the bike, with too little energy left for the run. For example, see our Ironman Coeur d'Alene Bike/Run Correlation Analysis. You don't want to end up in the 'Left it on the Bike Course' quadrant.