Signing in your first marathon is exciting thing. Filling up your details, you will come across question; What’s your predicted finishing time? If you haven’t run marathon before or there’s been a while since you have run one and your fitness level has changed, you might wonder what to put on that section. Organizer often want to the predicted finishing time, as there are number or color coded starting section. Each section presents certain finishing time, for example all runners who wish to finish under 3 hours are in the first starting section, then runners who wish to finish 3:01-3:30, and so on. Section are often divided every 15 or 30 minutes. This ensure that faster runner start at the front.
How you know where to start if you are first timer? Well, no one can know their finish time advantages, not even experienced runners. Marathon differ so much from training, there are other runners, nerves, possible new route, and a lot of other things which play a role. You might have well-prepared and everything does well until your stomach or legs cramps, or the weather turns out to be rainy and cold or extremely hot, these can affect your time remarkable.
Internet is full of calculator which predict your finish time based on your pace in the shorter distance. One of the most popular one is Peter Riegel’s formula, it can be used to almost any distances.
T2 = T1 x (D2/D1)^1.06
D1 = the distance you have already run
T1 = the time it took you
D2 = the distance you are about to run
T2 = the predicted time
Still, formulas and online running calculators are not 100% accurate, they can vary a lot and predict your finishing time even 30 minutes wrong. This is because formulas are based on the calculate your average running pace, adding certain amount of extra time every time the distance increase.
I would recommending use your training and timing when predicting your marathon time. During your marathon training, you should do the several long runs, which are close to the marathon distance. Record these runs, write down, distance, time, average pace, how does it feel like and route profile, is it flat, hilly … Compare these to your up coming marathon profile, whether the route is hilly or flat, think how much that will affect to your pace. Your own training runs are the best predictors. If you have run half marathon before, just don’t double that time because it’s unlike you can maintain the pace the whole marathon distance. Double that time and add some extra to it.
Finally, it doesn’t matter if you have predicted your time slightly wrong everything can happen during marathon. If the organizer use 30 minutes starting slots, they are big, so if you feel unsure about your predicted time go to the back of the slot and if you are very confident you will mash your time go to the front.