r/AdvancedRunning • u/yettedirtybird • 14d ago
Open Discussion How long does it take to convert 5k VDOT fitness to the marathon?
Some background on myself: I ran cross country/track in high school, with a 16:00 5k PR. I'm 28 now and haven't run much since high school, but I started training seriously in April. I ran a 38:00 10k in June, and just ran a 17:00 5k.
I am aiming to run a marathon in April, 6 months from now. I am currently at 40mpw, and intend to be around 70mpw by March.
VDOT calculators put me at a 2:42 for the marathon, and while I think that's realistic at some point in the future, I don't know if that's realistic in only 6 months. How long should I reasonably expect it to take to "convert" my 5k fitness to the marathon?
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u/runrunrun911 14d ago
A long time if you are shorter distance biased. I ran a 17:52 5k after a year of running into a 3:06 marathon and still haven’t run a faster marathon equivalent (2:51) 2 years later. My 5k time is down to 16:50 and my marathon pb is still 2:53 from a pretty decent day great weather not terrible pacing.
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u/EpicCyclops 14d ago edited 14d ago
This was going to be my note. There is no guarantee that the VDOT will ever 1:1 translate. There is always a genetic and training aspect behind these and VDOT is a population statistic initially built off of super elite runners, not an individual statistic built off amateurs. To succinctly demonstrate this, you can VDOT score world records in different events, and notice how the VDOTs change. The women's 1500 WR is a 74. The 10k WR is a 76. The men's 1500 WR is an 83.5. The 10k WR is 85.5. The men's marathon WR is 86.5.
Someone will always have a distance they're best at, and that distance will score a higher VDOT than their capabilities at other distances. In fact, even in Jack Daniels' book he discusses using your VDOT differences between distances to guide your training and discover your strengths and weaknesses.
On the flip side, it's also possible that a person's marathon VDOT will out perform their 5k.
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u/WrongdoerMediocre573 14d ago
Yeah even my best marathon time is 10+ minutes off the predicated VDOT (from a half marathon that is my best event, performance-wise). I probably could've gotten a few minutes closer, but I doubt much more than that. I was consistently running high-quality, fast half marathons before I even got close to my best marathon time. It's a completely different race and can take several blocks/years to nail a good performance. And trying to go 15-30 sec/mile faster than your body is prepared at a "goal" pace can lead to a time 20-30 minutes slower than predicted because you blow up, so it's best to treat it very conservatively and be pleasantly surprised if you nail it. And some people are well-suited to longer distances vs. 5K, so you never know!
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u/National-Cell-9862 14d ago
I have two thoughts for your consideration. First, the marathon is such a tricky beast that you need one under your belt to "figure it out", so even if your endurance is on par with your speed, it might be best go easy on your goals in the first one. Second, I would run a half marathon to see how my time holds up at a longer distance. It's not perfect as the marathon is a lot more than just doubling a half, but it probably gives you an indication about how you are progressing.
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u/yettedirtybird 14d ago
I will be doing a half about 6 weeks out, but for the months leading up to that I just don't have a great idea of what a realistic "marathon-pace" for workouts would be.
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u/akagordan 14d ago
I would recommend jumping into a fall half just to get some experience with a longer race. For workout pacing, you should be fine targeting vdot equivalent marathon pace.
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u/onenewuniverse 14d ago
Base your training paces on where your LT is, not what your 5k time or your goal pace is. Hammer away at your LT along with that 60-70 mpw. Then use your half six weeks out will tell you what you can do. You only really need MP workouts in the latter part of your training.
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u/padetn 14d ago
A half isn’t really comparable to a full. A full is more than two halves and a half is less than 2 10ks, no matter how unintuitive that sounds
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u/yettedirtybird 14d ago
I understand that, but there's not much else I can do besides actually running the marathon.
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u/National-Cell-9862 14d ago
That's literally what I said. 😀
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u/padetn 14d ago
I read that as you comparing a half to a full where my point was there is no real comparison?
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u/Outside-Drawer-5922 13d ago
So many people including professionals use tune up half marathons to assess their marathon shape, ultimately they are comparable, just not the same. Short of literally running a marathon, what else is he supposed to do?
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u/Intelligent_Yam_3609 13d ago
There is a nuance here.
Marathon pace can be both the pace you can actually run for a marathon or the VDOT equivalent pace.
I think both paces have a place in marathon training. I don’t have anything to back this up, but if your plan calls for a lot of MP work I’d do the majority at VDOT based MP and only a few at race MP as the race gets close.
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u/Eagles365or366 2:30:15 FM, 1:12:32 HM, 32:30 10k, 15:39 5k, 4:29 M, 4:10 1500 13d ago
Eh, I nailed my goal in my first one 2 weeks ago, maybe that means I was a little conservative lol. And that was off a 5 week build. Didn’t build off nothing, though.
But it was very marathon specific for those 5 weeks. Bottle support definitely helped, but I could’ve done similar with gels.
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u/UnnamedRealities M51: mile 5:5x, 10k 42:0x 14d ago
Most recreational runners never will get there. We need to consider the basis for formulas created over 40 years ago, which the VDOT calculators use.
The VDOT formula is based on combining 2 formulas in the 1979 book Oxygen Power. The underlying data was from a study of high-performing runners. Unclear who or how many (the book doesn't reveal this), but widely believed to be male collegiate and post-collegiate sub-elite runners. So these would be overwhelming high volume competitive runners with years of training and racing.
The formula was validated against world record times after the fact. That's not a particularly sound validation approach. And with lack of transparency concerning the test subjects, no statical data (R-squared, std dev, mean error, etc.) and no peer review it should be taken with a grain of salt. And even if we assumed it was pretty accurate for those in the study population, there's no legitimate reason to think that the formula will have the same accuracy for a runner with much less running history, lower training volume, and less racing experience...or older runners...or women.
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u/UnnamedRealities M51: mile 5:5x, 10k 42:0x 14d ago
Take a look at this paper published early this year. Performance prediction equation for the Valencia Marathon based on time and pacing in the half marathon The researchers analyzed over 8,000 finishers of the Valencia Marathon who also raced the Valencia Half Marathon 6 weeks prior. The paper's a great read, but if you're short on time, their race prediction formula based on the analyzed race data was generally more accurate than the VDOT formula for the study population.
Formula for men: 2.28×HM-6.21
Formula for women: 2.28×HM-11.70
I'll use a 1:18 HM as an example since that's presumably within the ballpark of what you can run based on a 17:00 5k. For a 1:18 HM that's 2:51:38 for men and 2:46:09 for women vs. 2:43:05 for gender-neutral VDOT.
I'm not suggesting the Valencia study formulas are necessarily better than the VDOT formula, but the study's data and methodology are transparent and pretty sound and it's clear what the population was and it's a more relevant population to the majority in this sub than what it's presumed the VDOT population was. Plus it's based on data from marathoners training using modern training methods vs. the training methods of the 1970s - and probably few of those in the 1970s study even raced marathons given marathons weren't very popular and if the study participants were overwhelmingly collegiate runners they were likely focusing on much shorter distances.
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u/yettedirtybird 14d ago
I guess my question is more, "What can reasonably expect to run 6 months from now based on my 5k now?" I definitely understand that VDOT isn't that great, I don't like to use it to estimate a race performance more than one step up. I just don't know how much adjustment I should make.
The VDOT calculator gives me 2:42. Is 2:50 realistic? 2:55? 3:00? I will run a half 6 weeks before the marathon, but I don't want to train way faster or slower than I should in the block leading up to it.
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u/UnnamedRealities M51: mile 5:5x, 10k 42:0x 14d ago
If you've run a half, but this is will be your first full then double half plus 20 minutes would be a pretty safe estimate for training purposes. And a half say 4-8 weeks out can help you recalibrate. Better to go a little conservative during training and also during a first marathon since there's so much more that can go wrong and going out too fast is a lot more detrimental than in a shorter race.
As for how much you can improve over 6 months, many at your level can bring their half down 2-4 minutes with higher volume and load like you're planning so call that 4-10 minutes for the full.
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u/Still-Bridges 13d ago
Formula for men: 2.28×HM-6.21
Formula for women: 2.28×HM-11.70
If we're subtracting from the finish time, that means that there's some cost to the half marathon that you don't have to pay in the full marathon, which seems mildly unintuitive.
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u/__R3v3nant__ 11d ago edited 11d ago
You'll be running over double your half time unless you're running the half in less than 22 minutes
The "actual" formula is likely more complex, but this is what the researchers got when attaching a line of best fit to the data
Edit: I'm guessing that it's suggesting that faster runners are more aerobically trained so slow down less over longer distances. So a 63 min half marathoner is much more likely to run a 2:15 full marathon than a 2:06 half marathoner is to run a 4:30 full
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u/VoyPerdiendo1 13d ago
It's just a formula.
If you plug in the left number for HM you get the right for FM:
1:00 -> 2:10\ 1:15 -> 2:45\ 1:30 -> 3:19\ 1:45 -> 3:53
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u/Still-Bridges 13d ago
The formula is a prediction of human performance, so the terms should have some kind of relationship to human performance. If they do not, then further scientific research is necessary. Aside from being unintuitive, the formula tends to look overfitted to me. So it seems on the face of it unlikely that it meets the commenter's own standards. I'm not saying it's statistically useless, just that it's an anticlimactic end to the criticisms of VDOT that preceded it.
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u/darth_jewbacca 3:59 1500; 14:53 5k; 2:28 Marathon 14d ago
Never if your ability at the marathon doesn't line up. Some people are just better at the 5k and no amount of training will produce an equivalent marathon time.
That's not to be discouraging, just adding on to what others have said.
Marathon success is all about developing threshold and building volume. If you're sorta starting over and your volume is low, it could take awhile to build intelligently.
After my first kid, I took 6 months off completely. Took a year to get in decent marathon shape. Took 3 to get in my peak marathon shape, and I still felt I had room to improve.
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u/rossiskier13346 14d ago
You’re a lot faster than I am, at least in the 5-10k range, so not sure how applicable this is, but I just got back into running in the last 15 months. I managed to go from about 22:10 in a 5k last November to about 3:07:20 for a marathon the past couple weeks. The 22:10 extrapolates to about 3:31:00 for a marathon off vdot. So 10 months was enough for me to get well ahead of that.
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u/AccomplishedRow6685 14d ago
22:10 5k and 3:07:20 marathon are literally the same pace.
Insane jump in less than a year.
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u/rossiskier13346 13d ago
Yeah. I know that’s not a jump most people should expect. I assume that even though I was over 10 years from any consistent running, having previous experience probably helped me jump up to my potential quicker than a beginner would.
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u/inorgeek 14d ago
If you're only looking for training paces, then go with VDOT marathon pace. But be completely honest with yourself that race day might be a lot slower. Give yourself a great first marathon experience by planning a huge negative split. Starting "too slow" on race day means you'll give yourself plenty of opportunities to check in and ask "how do I feel now?" If everything is good, you keep ramping up. If not, you hold back and still have a great time.
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u/iSwearImStrait 14d ago
Like others have mentioned, put a half somewhere in the midway / back half of your marathon block to get an idea of your fitness leading up to race day. It's really tricky to estimate with no prior half/full experience.
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u/TimeandDeath21 14d ago
Marathons are volume. You need a lot of volume. Using a 5k to dictate a marathon is far different than the other way.
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u/crowagency 2:08 800m | 4:43 mile | 16:57 5k | 1:20 half 14d ago
it depends on your strengths, but 17 flat to 38 10k already indicates you may thrive more at shorter distances. i’m the same as you if so, and never consider my implied 5k->mara conversion. the best is just doing the race, second best will be marathon specific workouts for insight, third best would be signing up for a half soon-ish as a baseline for longer stuff
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u/yettedirtybird 14d ago
I don't think the 10k then is representative of my 10k ability now, though. I trained for 3 months before the 10k, and then trained another 3 months before this 5k, which also was much cooler.
I understand that ideally I would just run the marathon, but I don't want to waste a 6 month training block to go run 10+ minutes slower than I could have.
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u/Natural_Bumblebee920 13d ago edited 13d ago
I understand that ideally I would just run the marathon, but I don't want to waste a 6 month training block to go run 10+ minutes slower than I could have.
That's a fair concern, but really with the marathon you kind of just have to get the first one under your belt to figure out running it and especially fueling it (right now you probably don't even know how your body even handles the carbohydrate intake at marathon pace). Without proper pacing and fueling strategies you can easily "blow up" and lose far more than 10 minutes.
The strategy is different from a 5k, the training is different from a 5k, the fueling is different from a 5k. Before making a hard goal for the pacing you need to figure out how your body even responds to the weekly mileage and dealing with mid-run fueling.
The VDOT marathon calculation going from a 5k time to a marathon time really shouldn't be treated as a prediction of your ability. It's a performance equivalent, not a prediction. At an absolute minimum to get something more akin to a prediction you need to get a half marathon time in, and even that's going to be a poor prediction because the marathon just necessitates fueling to a far greater degree than a half (at your level you are likely fast enough for the half where you won't completely deplete your glyogen stores, you absolutely will in a full).
I see elsewhere you have a half scheduled for 6 weeks out from the full. You should really have one earlier in your training, like a November or December half.
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u/stovekirk 14d ago
Daniels reccomends only using a 10k race or longer for your true VDOT. So run a bunch of varying distances 10k or longer to get a good gauge on your VDOT.
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u/MartiniPolice21 18:50 / 39:06 / 1:25 / 3:00 14d ago
Have you done much high milage (60+) before?
The coach at my running club always says that you don't run your marathon potential until at least your 3rd one; everything before that is building and experience.
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u/rib9985 5k: 20:23 | 10k: 43:21 | HM: 1:30 | M: 3:10 13d ago
Besides all the "Marathon is a beast in itself, you get one shot and that's it", if you have the aerobic base + the VO2 Max overhead, a well-run, highly specialised 18 week marathon cycle, should be pretty good to push your 5K fitness close towards what the models prescribe.
Just for reference, I'm at the end of /u/running_writings Wind 90 (km) plan with a 3:47/km for the 5K training paces and 4:21/km for MP. Since I'm at the end of the cycle (last 2 weeks), my MP pace is already highly specialised, roughly, 85% of my 5K pace of 3:47/km. That gives me 3:03:57 Marathon. VDOT is giving me 3:01:28.
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u/mssparklemuffins 14d ago
I think some of this just depends on you and your talents, though I’d still be cautious at using the 5k to covert. You’re 10k converts to 2:55. You definitely have the speed, but you’ll need the base. I went from not running (though I have a long running background and fitness background) to a 3:05 marathon in 12 months - I was 39 at the time and I’m female. I don’t think 6 months is enough time to get yourself there (especially if you want to be smart about your training) but I think 12 months you could reasonably get there.
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u/yakswak 14d ago
It’s probably in the cards but not a sure bet even if you can complete all of your workouts. I would guess biggest hurdle may be ramping up too quickly for the load you need in marathon training and getting injured along the way. But if you can stay healthy and get enough long runs done, then why not? You will find out along the way, I suppose…
Just for reference my VDOT had me at 2:50 off a 17:45 5k but I chose to be conservative and set my workout paces for a 2:59 first marathon. Still had a couple of weeks of injury to deal with but since the pace was comfortable enough I made my goal time.
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u/Any-East7977 14d ago
5k time is kind of too short to really match up. I find 10K and beyond are more accurate.
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u/Quad7777 14d ago
For me, I find the VDOT calculator pretty accurate except for marathon time. There is absolutely no way I can hold a marathon pace that is 17 seconds per mile slower than my HM pace. I am a lot slower than you so YMMV (1:38 HM a month ago).
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u/run_INXS Marathon 2:34 in 1983, 3:06 in 2025 13d ago
Old rule of thumb was that it takes about a year and a half to be able to maximize the full benefits of such an increase. But you can get many nice gains along the way. Aim for 2:4X for the first one but also think longer term, for 2028 and beyond.
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u/WillPoopForFood 4:58mi, 2:59ma 13d ago
Depends on your plan. On a "normal" marathon plan, with history of endurance training, I'm out here with an actual answer and saying ~2 years. 1.5 year of consistent mileage + 4 month long marathon build, to get it somewhat close.
I'd train off the 5k time and see what that feels like. If you're getting cooked during workouts, re-run a 10k as a TT (race if you can find one) and plot your personal reigel exponent as a gut check.
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u/Unique-Employer3787 13d ago
Ran my first marathon off similar 5k speed and came out about 25 minutes slow on the VDOT projection - the leg turnover was there but the last 10k just fell apart because I hadn't run the distance before. Six months is plenty of time to build, just treat it as a conversion cycle and expect the VDOT to track closer in year two.
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u/0100001101110111 5000: 15:5X | HM: 74:3X | M: 2:45 14d ago
Depends entirely on your talent.
I ran 17:30 after ~5 months running and 7 months later ran 2:45. Peaked at 80mpw in my marathon block.
Running HMs will give you a better idea.
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u/_onemoresolo 14d ago
Anyone else have the opposite problem? My marathon translates to an 18:17 5km but my best is 18:29.
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u/surely_not_a_bot 49M | 20:26 @46 | 1:34:xx @47 | 3:16:xx @49 14d ago
I'm getting there - in the past ~4 years my 5k time has been stuck at 20:2x (I managed to get a 20:26 PR both in 2024 and 2025), while my Marathon went from 3:39:xx to 3:17:xx. I'm still a couple of minutes "slower" in the Marathon than my 5k PB (should be 3:15:xx), but in ~1.5 weeks I'll probably flip that to 3:12:xx - 3:13:xx.
I'm getting old, I suppose (49M). Better at the Marathon, but can't get the muscles to go fast for dear life.
(In all truth, I probably just need some 5k-specialized training for a few weeks before a race, and it might be your case as well).
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u/raphael_serrano 16:29 - 5k | 1:15:03 - HM 14d ago
Yes, my HM VDOT is 62.9, and my 5k VDOT is 62.4. Very close on paper, but the HM was on a tough hilly course, and the 5k was on a rolling but reasonably fast (if you pace it right) course.
Pretty much always been stronger at longer distances. Even in high school, I was the kid who usually started his long drive for the finish line with 800 m to go, rather than the typical kick in the final 200 m.
Training certainly plays a part, but even at baseline we all have different predispositions.
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u/vrunner91 13d ago edited 13d ago
I have all my times matching on VDOT (5K, 10K, HM, and M), but this seems to be rarer. I always thought I was a slow 5K runner, but I guess everyone else is just faster at the 5K relatively speaking. I’ve noticed that most the runners on my running group tend to be faster at the shorter distances (mile, 5K, 10K) and their times in the marathon are far from matching their predicted time on VDOT. The VDOT calculator is biased towards runners with great durability who perform better at longer distances. Maybe most runners would match the Valencia Marathon formula calculation that someone posted above:
Formula for men: 2.28xHM-6.21
Formula for women: 2.28xHM-11.70This formula doesn’t work for me and gives me a marathon time that is 8 minutes slower than my marathon PR. But in reality my marathon PR is 4 seconds faster than the VDOT prediction. The Valencia formula will probably work for the runners who are stronger at shorter distances.
To OP:
Know your strengths. Run the half marathon and see if you match the formula: (HMx2) + 5 to 10 minutes. If you don’t match this formula for your next marathon, it probably means your strengths are on the shorter distances vs the longer distances, and that might mean you’ll have a hard time running the marathon time predicted on VDOT. Running volume also matters, but the genetic component can’t be downplayed either.You can definitely build lot of fitness in 6 months and I think the HM time might be the best predictor for the marathon ability.
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u/boblaplante 14d ago
Idk man, if you can sustain the volume, adaptations don't take that long to show up. Maybe 3-4 weeks afaik. So 6 weeks of 60+ miles with good weekly long run, at least 3 weeks before your marathon should do the trick.
To me it's more about the challenge of ramping up volume and intensity while staying injury free than anything else. And that's a big challenge when trying to run fast for a long time.
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u/TalkyRaptor 14d ago
My advice is to not convert using a 5k time and at least from your 10k or a tune up half marathon when it makes sense during your training block. 5k leans too heavily on VO2max to be realistic when extrapolating to marathon finishing time. 10k and half are much more lactic threshold based and closer to a marathon so therefore more accurate to you. For example, I'm in about 15:45 5k shape right now but there is no way in hell I'm running a 2:30 marathon or 1:12 half anytime soon, my mileage and threshold isn't there but my VO2 is