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Marathon Prediction Model

To provide guidance on pacing, I have calculated the performance ratios for two “event pairs” for a sample of runners. These ratios can provide guidelines for your next marathon target. Bottom line, a faster/improved time at either the 10K or Half-Marathon should translate up to a faster time at the marathon, all other things being equal (mileage and other workout metrics). For these two pairs, the lower the ratio, the more efficient you are in running a marathon and the lower the event/marathon ratio, the more efficient you are in pacing your marathon.


The table should help answer the question, “What is the relationship between a half-marathon time and a marathon time?” Or, “How does a faster Half-Marathon translate to a faster marathon?”


Although there is a statistical correlation between the half vs. the marathon, as illustrated by the Jack Daniels VDOT chart, I believe there is a direct “cause and effect” relationship between the two performances. Basically, if you can run the chart-time for the half marathon you will be more likely to run the associated marathon time. 


The Daniels chart associates 1:14:54 with 2:36:44, so the minimum standard for 2:37 marathon is a sub 1:15 half. With this being said, it is still possible to exceed the predicted values/have a marathon breakthrough if your training block goes exceedingly well but you lack racing data points. However, competitive data points at both the 10K and the Half-Marathon provide both information and training value and are essential in the Marathon buildup.


In this discussion, there are a number of possibilities that could yield a faster marathon.




First, improve your pacing strategy without actually improving your 10K or Half-Marathon – Alternative Scenario – if you see no improvement in your half-marathon and/or 10K in your build-up.


If your pacing has been problematic – either too aggressive early in the race or erratic during the race, having to involuntarily slow down over the last 10K, you can improve your time by cleaning up your pacing without improving your fitness. This can be done by starting more conservatively or avoiding “cat-and-mouse” racing behavior or arbitrary surging strategies. Theoretically, you should be able to run faster without improving your fitness, but you still need to adhere to your historical ratio in prediction your time and pace. Exceptions.

Second, improve your 10K/Half-Marathon and still pace problematically – Alternative Scenario - Not recommended


This assumes that you pacing strategy does not change but your training and racing improve.


Third, improve your Half-Marathon Time and concurrently your pacing – Recommended Scenario 


A good metric for evaluating pace is the “standard deviation” statistic based on your marathon 5K splits/statistical arguments. 


The closer to even pace you run, the lower the standard deviation, and the more efficient is your pacing, hence increasing the probability that you will run a faster time. The subtext at play here is purely exercise physiology – the efficient utilization of available energy and the readiness/conditioning of your physiological systems based on your training. Burning too much of your available glycogen early combined with overstressing your other systems, including your digestive system/ability to metabolize fuel, will most likely not produce the desired outcome.


The objective is to predict your marathon time based on your most recent training and race times, applying your historical ratio, and executing an even-pace or a slightly negative split race plan. This is where the ratios come in. I recommend using your historical half-marathon to marathon ratio in predicting your marathon time. The math is easy, having faith in the number and sticking with the plan is difficult. 


Inevitably, you will feel good at the half-way point and the temptation to push the pace beyond your capacity/fitness level may override your good judgement and commitment to your plan.


Succumbing to this temptation/abandoning your plan could end in disaster. You will not only pay the price of pain/death-march experience in the race itself but you will eventually have to explain, justify, and defend your decision to your coach, your peers, and to people you don’t even know.


Of course, in planning your race, you must factor-in the course and the conditions. If they are favorable, you have a much better chance of hitting your goal. But my advice is to choose a proven fast course, such as CIM or Grandma’s Marathon, if you are shooting for a PR. If you are in it for some other reason than running fast/PR, none of this really matters, stop reading this, pick a bucket list race, go run, have fun, and enjoy the experience!


The Standard Deviation (SD), mentioned previously, is based on 5K marathon splits. The lower the value, the more even-paced the race was, hence the more efficient was the pacing/utilization of energy.


Here is a sample of the Standard Deviation from the 2022 NYC Marathon. The lowest value was associated with Emma Bates while the second was Aliphine Tuliamuk. Although Aliphine’s SD value was higher, and ran faster than Emma, she slowed down more in the final few miles.


Screenshot 2023-07-08 7.34.56 PM.png

Notwithstanding my long-winded dissertation, here is the ratio-based goal setting process:

  1. Calculate your recent Half-Marathon to Marathon Ratio. 

  2. Apply that ratio to your most recent Half-Marathon to calculate your target Marathon time.

    1. Pick a fast course and factor in the course characteristics and weather conditions

  3. Stick with the above ratio calculation and stay on your plan.

Note – A PR or Personal Breakthru can be most easily accomplished with even-pace or a negative split race plan.

I do not recommend a “Cushion” strategy, i.e. running “positive splits” – this is more likely end in a painful train wreck. 


The chart below provides ratios that can be applied to race plans over a spectrum of marathon times, from 2:19 to 2:42. The ratios range from 2.05 to 2.12, Half-Marathon to Marathon, for the sample,  


Information, assumptions, logic:

  • All performance numbers are from World Athletics – best recent times were used for the chart calculations.

  • The lower the ratio, the less is the per mile differential between either the half-marathon or the 10K and the marathon pace.

  • The Jack Daniels ratios are identical for the 3 highlighted Marathon Times. 

  • The Jack Daniels VDOT-based ratios would suggest that a sub-1:15 half or a sub-34 10K would predict a sub 2:37 marathon.

  • I carry the decimal out to 1/100 because a .01 delta = about 43 seconds deference over 26 miles. If you improve your ratio by .01, you could run 43 seconds faster.

  • If you don’t have either a half-marathon or marathon time, default to the Daniels VDOT chart with the associated 10K time for your prediction.

  • This prediction model assumes that your marathon training – mileage, long runs, intervals – have been at least as strong as previous build-ups.

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