Why Half Marathon Times Don’t Translate into Full Marathon Times

Here’s a question I received from a fellow runner named Chris,

Hi Angie! I’m 50 years old and have been running for 2 1/2 years (after losing 105 pounds, but that’s another story). My times for the half marathon are decent, generally in the 1:55 area. I’ve run three marathons with a PR of 4:27:34 and a worst of 4:58:30.

Anyway, based on various race predictors, it looks like my “expected” marathon time is in around 4:05. Why am I so far off, and how can I get my half marathon ability, such as it is, to translate to the marathon distance? I’m training for the Long Beach (Ca.) Marathon in October and I’d really like to come in around 4:10 or so. Thanks, and keep up your great work! -Chris

My answer . . .

Why Half Marathon Times Don’t Translate into Full Marathon Times

First of all I’d like to thank Chris for the question and congratulate him on taking control of his health and fitness!  Looking back on what he has accomplished already should give him the confidence to realize that he can reach his goal of a faster full marathon.

Chris is definitely not alone in feeling this frustration. Many runners have been disapointed to realize that online time predictors don’t necessarily hold up under real world conditions.  The ability to run a fast half marathon doesn’t always equate a desired marathon time. 

  • Various factors like the intensity of your training, weather conditions, how challenging the course is, how you’re feeling on race day, fueling, mental toughness, etc all play into the marathon time you’re able to achieve. What’s more, it takes a more advanced set of physical adaptations to run a full 26.2. You have to master the art of running (an maintaining your goal pace) on tired legs.

Algorithm based time predictors cannot adjust to take these individual challenges into consideration. A more accurate way to estimate your marathon time would be to put a recent time from a 20 mile run into the calculator.

In Chris’s case, in order to have a better chance of achieving a 4:10 marathon it will be important to do regular speed work as well as some paced long runs. 

It’s also a good idea to include 2-3 twenty mile long runs into your training cycle.  This way your body will be better prepared for the marathon distance.  You’ll be able to dial in fueling as well as work on developing mental toughness. Also, look at addressing any issues that may have slowed you down during previous marathons.


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