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The McMillan Running Calculator

Have you ever finished a 5k with a new PR under your belt and thought to yourself: “If I just cut 1 minute off my 5k time, how much time could I slash from my marathon?”


If you’re anything like me, your answer to this questions would be: every single time.

Enter: The McMillan Running Calculator.

The McMillan Running Calculator was created by Greg McMillan after he grew increasingly discouraged by the inaccuracies of other running pace predictors. While I cannot speak to the science behind his approach, I can attest to the fact that his little invention has been a bit of a training bible for me during my running career.


The way it works is you plug a time and distance into the calculator and it spits out your predicted race times in every distance imaginable.

I use this in two ways.

First, (and most frequently), I input my goal marathon time and see where it thinks I should be for every shorter race distance.

As you know, if you’ve been reading my blog for more than a day, this is currently a 3:19.59


After the distance is selected and the time is entered, you hit calculate, sit back and watch the magic happen.



Now I know that the next time I race a 100m, I should aim for a 17.4.

Or, in more useful news, my half marathon time should be around a 1:34.49.

While I know this may not be rooted in exact running science, I used it as a reference point while I was trying to hit my first Boston Qualifying time at the Chicago Marathon and it proved itself to be an accurate and useful tool as I raced shorter distances leading up to my BQ marathon. If nothing else, it gave me the confidence I needed to believe that the BQ was within my reach.


I will often spend race day mornings sitting at my computer, inputting various times to try and help me form a goal for my performance. Yeah, I’m not obsessive at all…

The other way I use this running calculator is to take current PRs and see where it predicts me for other distances.

Obviously, the moment I got home from yesterday’s 8k, I immediately consulted my good friend McMillan to check out his analysis of my new PR.


Turns out, dear old Greg believes that based on my 32:57 8k race, a sub 3:20 marathon is well within my reach.


And no, I don’t think I’ll be running a 3:14 in Philly but it does give me faith that my sub 3:20 goal is going down.

The other benefit of the McMillan Running Calculator, is that it gives you some guidance as to what your training pace should be for various runs (tempo, track, recovery, long) based on your current PRs or your goal time, depending on which you’ve got plugged in.


I use this less frequently since there are so many other guides to training paces out there but I do consult it as another way to gauge if I’m on track for my goals.

Do you ever use a running pace predictor? Do you guy into them? How is this kind of a tool most useful to you?

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22 Responses to The McMillan Running Calculator

  1. I use McMillan and some other race predictors as rough guides both for race predictions and guidelines to training paces it would be good to hit. I don’t think it is an exact science and does vary by person how accurate it is. I find I tend to overperform in longer distances (or underperform in shorter distances for the pessimistic view), but it still is a useful tool. And like you probably spend too much time playing with it…it is fun!

  2. I play with this and the Jack Daniels calculator (http://www.runbayou.com/jackd.htm)….oh, everyday?

  3. It’s funny that you started this post with a PR about a 5K because I finished a 5K today with a new PR under my belt!! And that calculator is pretty cool!

    xo Marie
    Chocolate & Wine

  4. I love McMillan Running. I use it for my personal goal setting as well as to help me guide clients to the right training paces etc.. I found another one that I like as well. It says that it bases the times on a calculated Vo2 max value. You might enjoy it. http://www.attackpoint.org/trainingpaces.jsp?dist=26.2&units=miles&time=34800

  5. I use Mcmillan, too. Seems to work for me :)

    Can’t wait to hear about your sub-3:20!

  6. Great post! I do the exact same thing. As soon as I got home I plugged the 8K time into McMillan and out spat a 3:32. My goal is a 3:35, so I think we are both in the same boat of just having the confidence that our goals are well within our reach. I’ve been accused of relying too much on that calculator, but as long as the racing conditions (weather) are relatively the same, then I have found McMillan to be dead on.

  7. I have used this a lot in the past, as a reference. I never knew exactly how reliable it is, but after this post (and some of the commenters) I have more faith in it. I’ll have to check it out again.

  8. I have never used McMillan running calculator but I should check it out! I have used some other pace calculators to figure out what pace I should go if I want a specific time, though. I like the different options that McMillan provides, seems like I would spend way too much time on it (like I do with almost anything related to running).

  9. I’m also kind of a little obsessed w/the McMillan calculator. Basically, I love anything that allows me to indulge my fantasies of becoming a super-speedy runner. From a more practical standpoint, I find it super-helpful for figuring out my goal paces for tempo runs and intervals.

  10. I use this calculator too and love it.

  11. Ooo, I have never used McMillan. I will have to check it out! I like to use pace calculators when I am goal setting for an upcoming goal race. It helps me keep my goals realistic and something that I can work towards.

  12. Damn – I wish they had a geek or nerd race in NYC -I would ROCK THAT!

  13. Yeah, I kinda like the McMillan one. It certainly time-checks me. Sometimes I have lofty (the half) and other times I’m too conservative (marathon) with my goals. Based on the awesome 10K I ran this past weekend, he says I can do a 4:19 marathon next weekend. Wowza! Not sure about that, but it may give me a little confidence going into the race…

  14. i’m starting to be concerned you will run the full faster than I do the half…ok no seriously at least I won’t have to wait long to cheer you in :)

    You are in amazing shape and your motivation is what makes it completely possible for you to hit your desired time.

  15. that chicago shot is brilliant. nice headphones.

  16. I don’t really use these calculators much, but I think that as I start entering more and more races with a variety of lengths (instead of one or two marathons every once in a while), I’ll probably put them to use more often. According to this calculator, my 15k PR from yesterday puts me at 2:48 for the marathon…. which kinda makes me groan since that’s so stinking fast (it would be a half hour PR for me), but makes me think I need to shoot for a sub 3:00 in my next attempt. Maybe I’ll set a 2:55 goal???

  17. Thanks for the tip! I haven’t liked any of the pace converters I’ve seen. I will definitely check this out! Congrats on the PR!

  18. So i have used this and I like it but I am kind of scared of it. It says that I could run a really fast marathon, fast for me anyway. and it seems a bit crazy for me. I am running MCM in October, it is my first. i have no clue what my goal pace is. my goal is just to finish. but i really have no clue how hard i should go out or what to do. this weekend i did my long run and stayed at 9 min miles for the first 13 and ended with a 5k in 22:52 or something of that and felt like I could have done more…haha i am all over the map on this and my coach just says do your best. so yea…i want this to help, but just not sure if it can. do you like my random crazy comment? sorry! see the running enduced marathon crazies here.

  19. I am obsessed with McMillan also! It definitely has been right on before with everything from 5k to marathon, BUT it has also bursted some of my marathon confidence when a tune up race doesn’t go as well as I hoped. I think its a GREAT tool and one I have been using since I first started training :) looks like you have a good marathon in the cards ;)

  20. The calculators can be fun but they are really only accurate when comparing two distances that are somewhat close. For instance a 5k time cannot predict a marathon time if the person runs low mileage. Also a marathon time cannot predict a 1 mile time if the person only runs long slow distance.
    I think it can show what you are capable of if you put in the correct training for a particular race distance.

  21. […] Will’s pick is McMillan Running Calculator […]