The method of projecting a marathon time described in my essay titled “Predicting A Marathon Time” is based on training mileage and 10k performances, which was the most popular race distance of yesteryear when the database that I used was collected. One conclusion of my essay is that the ratio of marathon-to-10k race times for “average” midpack runners is about 5:1, as compared to the 4.6-4.7:1 that running calculators yield.

As half marathons (HM) have become more available and popular as a stepping stone to the marathon in recent years, their use as a baseline for projecting a marathon time has increased. Resultant marathon time projections of running calculators are likely to be too aggressive for most runners. And the rules of thumb of doubling HM time and adding either 10-miuntes or 10% is even more aggressive, especially for those who run HM’s slower than 1:40. Lacking any basis for relating HM and marathon performances, I suggested in my essay to convert a HM time to a 10k time using a running calculator, then use the mileage-based factors that are in my essay to project a marathon time.

A runner who’s screen name is Andre_Media on running forums conducted a study of 300 runners who ran HM-marathon combinations that were 6-8 weeks apart, such as the Philadelphia Distance Run and the Philadelphia Marathon. His report that follows presents the results of his study and suggests a guideline for projecting a marathon time from a HM performance that is probably more realistic than calculator projections for many runners. It is posted here with his permission.

Determine Marathon Pace on Real Results

Dan O'Donnell

The purpose of this piece is to share the results of a specific study that I conducted about setting a goal running pace for the marathon. I hope you find it to be useful and relevant information to make you a more informed runner. This is not a study of how you should train. More miles run consistently over time will make you a faster runner. Training for the distance and training to race the distance will improve your times. Nevertheless, I hope this offers some insight and another tool to help you plan an appropriate pace for the marathon race.

This is geared for anyone preparing to run a marathon and who does not have a lot of recent marathon experience to draw from. The often asked question is; what pace should be run that will provide the best result? Marathon veterans can assess the quantity and quality of their training and usually know the answer. But there are many inexperienced marathoners that struggle with this question.

Attempting to answer this question is by no means a ground breaking notion. Running calculators have been established that help determine an equivalent performance at one distance based on performance at another. These calculators can be found all over the Internet. Check out McMillan Running or Runners World.

The running calculators are an interesting tool to tinker with. For those interested in the analytics of the sport, they offer much to consider. You plug in any time (depending on the calculator used) from 100 meters to 26.2 miles and they return a projected time for every distance imaginable. They also offer training paces that can be used for long runs, tempo runs, easy runs etc.

Some might eschew the use of such information and simply run. After all, much of what is done in athletics is done by feel and instinct. A good cross country runner will soak up the variables of the race: the competitors, the terrain, the weather and his own perceived effort and pain. Even though his coach is calling out his splits, the good runner already knows what is going down in the race. His instincts, not a Garmin and not a running calculator will determine his pace and he is feeling his way through every step of the race.

But the study that I conducted is not intended for a cross country race, but rather for a marathon. The longer the race, the less you can rely on feel and instinct to guide your actions and control your pace. This is never truer than in the case of the inexperienced marathon runner. For inexperienced marathoners, the need to rely on something more tangible than feel is even more important. First timers are often given the advice that the first marathon should not be run with a goal time, but rather to learn from the experience and finish healthy and strong. This is sound advice, but not so easy to follow for some.

The running calculators have become a prevalent tool used to gauge performance potential. But I have always been curious how they were constructed and from what results they were based. In my research, I have not found clear evidence that relates the formulas used in the calculators to actual race performance. Although, I speculate that somewhere there is a database full of race times for athletes, probably elite athletes from some time ago. Furthermore I suspect that there is a lot of extrapolation built into the formulas. How else could one correlate the results between a 5K and marathon?

From my reading on the subject, I realize that the calculations are generally thought to be optimistic at projected race times for longer distances. Furthermore, they state that there is an assumption that the runner is adequately prepared for the projected distance. Most will agree that the closer the two distances are to each other, the more accurate the projection will be. The study that I conducted was exclusively meant to correlate the half marathon distance to the full marathon.

While all of the calculators have slight differences, the results are statistically very close. The running calculator’s ratio of full marathon/half marathon is on average 2.115. I have not found any that were lower than 2.11 or higher than 2.12.

While I was reviewing these, I converted the results to minutes per mile. It was looking at the results in this way that caused me to dig a little deeper. The chart below shows the results of converting a half marathon race to a full marathon in terms of minutes per mile.

These are the average results of Runners World and McMillan calculators.

Half Marathon Time Half Marathon Min/Mile Projected Full Marathon Time Projected Full Marathon Min/Mile Difference in Pace 1:44:00 0:07:56 3:39:58 0:08:24 0:00:28 1:46:00 0:08:05 3:44:11 0:08:33 0:00:28 1:48:00 0:08:15 3:48:25 0:08:43 0:00:28 1:50:00 0:08:24 3:52:39 0:08:53 0:00:29 1:52:00 0:08:33 3:56:53 0:09:02 0:00:29 1:54:00 0:08:42 4:01:07 0:09:12 0:00:30 1:56:00 0:08:51 4:05:20 0:09:22 0:00:31 1:58:00 0:09:00 4:09:34 0:09:32 0:00:32

As you can see from the results, according to the running calculators, the mid level marathoner should plan to run the marathon at approximately 30 seconds per mile slower than the half marathon. I thought these results to be more than just a little optimistic as a baseline. Surely some will achieve this ratio, but I thought the averages would result in a larger difference in minutes per mile.

I conducted a short study of the results from the Philadelphia Marathon together with the Philadelphia Distance Run (Half Marathon). In this case the marathon is run about 8 weeks after the half marathon. I speculated that many people would run both, and most of those that ran both, were running the half marathon in preparation for the full marathon.

I downloaded the results of both races and used MS Excel to sort and do a lookup from each set of results to come up with matches of those who ran both races. For the purpose of this short study, I excluded those that finished either race in the top 10% or bottom 10%. Using the actual results of these runners, the ratio of time between full and half marathon were very different from the calculators. The average factor was 2.25. The average difference in pace was a full minute, which is double what the calculators suggest. Since the results were so different from the calculators’ projections, I tried to come up with an apparent flaw in my assumptions.

What if some of these runners didn’t ‘race’ the half marathon and approached the half as just a long training run? Well that would sway my results to an even larger variance from the calculators. There are of course other factors, such as the training habits of my result set and the weather for the event that are important determinants in pacing and times. In attempt to account for other variables, I knew I needed a larger and diverse population of results.

I expanded the sample size and went through the same process with races in six other cites: Dallas, Columbus , Portland Or, Nashville , Wilmington De. I used results from 2008: some of these were spring marathons and some were in the fall. In all of these cases, the half marathon was run between six and eight weeks prior to the full marathon. The resulting factor came down slightly to 2.23. I also expanded the search by removing my exclusion of the top and bottom of the field. There was no material difference in the resulting ratio. After expanding the analysis, my sample size was over 300 runners and the average pace differential for those running in the 3:40 – 4:20 marathon time was approximately 55 seconds.

I think the implications are substantial. Take the case of the mid-packer (like me) who runs a half marathon at 1:48. He goes online, plugs in his time and is delighted to see a projected finish in the 3:48 range for the marathon. He sets out to run a 8:43 pace which starts to fade halfway through the race and is in shambles by mile 18. Based on the results of my study, he should have been running about 30 seconds per mile slower.

The table below illustrates what I think is a considerable variance between the suggested paces offered by traditional running calculators and my research.

Half Marathon Time Projected Full Marathon Time (based on calculator) Projected Full Marathon Time (based on research) Projected Pace for Full Marathon (based on calculator) Projected Pace for Full Marathon (based on my research) Variance in Full Marathon Pace 1:44:00 3:39:58 3:51:55 0:08:24 0:08:51 0:00:27 1:46:00 3:44:11 3:56:23 0:08:33 0:09:01 0:00:28 1:48:00 3:48:25 4:00:50 0:08:43 0:09:12 0:00:29 1:50:00 3:52:39 4:05:18 0:08:53 0:09:22 0:00:29 1:52:00 3:56:53 4:09:46 0:09:02 0:09:32 0:00:30 1:54:00 4:01:07 4:14:13 0:09:12 0:09:42 0:00:30 1:56:00 4:05:20 4:18:41 0:09:22 0:09:52 0:00:30 1:58:00 4:09:34 4:23:08 0:09:32 0:10:03 0:00:31

The marathon is an unforgiving race and the margin of error shown above of 27-31 seconds grows into something worse during the late stages of the race. In the middle of a marathon when you might realize you went out too fast it’s very tough to then just adjust to a new, more reasonable pace. The damage is already done and you will end up running slower, much slower. If you significantly outrun your potential during the early miles, it’s very difficult to avoid a painfully slow experience during the final miles. As far as your ending time is concerned, the seconds saved running too fast at the beginning of a race, will not be enough to balance out the eventual slow down at the end.

An experienced runner can certainly make adjustments to the pace during a race that will improve their end result. But the marathon is very a long race and the inexperienced runner may not get or understand the signals from his body soon enough to slow down and salvage a good time.

The baseline conclusion that can be drawn is that a mid level runner should expect their marathon pace to be approximately 55 seconds slower than their half marathon pace. The fact that I focused on the 3:40 – 4:20 marathoner might cause some to suggest that the runners in this study were probably not adequately prepared to run the full marathon. However, I used the most relevant set of data I could find: real runners, running real races with actual results.

There were 15% of the runners in my research who had marathon times equal to, or better than the projections from calculators. You might be one of those 15% but then again, you might be in the bottom 15% and should add ninety seconds to your pace. I would suggest that your training mileage would be the single largest determinant in where you fit on the scale.

Experienced marathoners who keep track of their training and race times from one season to next have the best measurement of marathon potential: personal experience. This study is offered to those who don’t have a lot of recent marathon experience. It is offered with the suggestion that if you are determined to run a marathon with a goal pace, you might want to give this a try. Run a half marathon race 6 – 8 weeks before the marathon and revisit these results. If you think the quality and quantity of your training was about average, go with the paces I suggest and add about a minute to your half marathon pace.

Good Luck!