Turn your average 800m repeat time into a rough marathon prediction using the popular Yasso 800s rule of thumb — a widely-shared piece of running folklore, not a scientifically validated formula.
Yasso 800s are a marathon training workout — 10 × 800m repeats at goal pace with equal-time recovery jogs — popularised by longtime Runner's World "Chief Running Officer" Bart Yasso. The associated "prediction" is a simple digit trick: your average 800m time in minutes and seconds is said to match your marathon time in hours and minutes (a 3:30 average predicts a 3:30:00 marathon). This is a fun, popular rule of thumb passed around running clubs for decades — it is not a scientifically validated predictor, and running scientists and coaches generally regard formula-based tools such as the Riegel method (used in our Race Time Predictor Calculator) as more evidence-based. The workout itself, however, is genuinely useful marathon-specific training regardless of how precise the prediction turns out to be.
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Bart Yasso spent decades at Runner's World magazine, where he became known simply as its "Chief Running Officer." Somewhere along the way — Yasso himself has told the story with a shrug, saying he stumbled onto the pattern through his own training rather than through a laboratory — he noticed that his average time for 800m repeats, run in a session of ten, seemed to line up numerically with his marathon finish time. The idea spread by word of mouth through running clubs long before it appeared in print, and it has stayed part of marathon training folklore ever since. It is important to be upfront about what this is: a popular, catchy training mnemonic that a lot of runners enjoy using, not a peer-reviewed or scientifically validated prediction method.
The workout behind the trick is straightforward. You run 10 repeats of 800m (roughly two laps of a standard track) at your goal marathon pace for those repeats, jogging an easy recovery between each one that takes about the same amount of time as the rep itself. So if you run each 800m in 3 minutes 30 seconds, you jog for roughly 3 minutes 30 seconds before starting the next one. The "prediction" part is just a unit-swap: whatever your average 800m time reads in minutes and seconds, read it again as hours and minutes, and that is your supposed marathon time. A 3:30 average becomes a 3-hour-30-minute marathon prediction. A 4:15 average becomes 4 hours 15 minutes. There is no underlying physiological formula converting one to the other — it is simply the same two numbers reinterpreted in a different unit, which is exactly why coaches describe it as a memorable rule of thumb rather than a scientific model.
Here is the honest answer: reasonably useful as a rough guide for some runners, and not reliable as a precise predictor for everyone. The "same digits" trick was never derived from physiology — it is a numerical coincidence Bart Yasso noticed in his own training that happened to be memorable and easy to repeat. Running coaches and sports-science writers who have looked closely at it generally agree it tends to land in a plausible range for many mid-pack marathoners with a fairly typical balance of speed and endurance training, but it becomes noticeably less trustworthy at the extremes. Very fast runners with strong raw speed but comparatively less marathon-specific aerobic base often find the Yasso method predicts a faster marathon than they actually run. Slower or less experienced runners, and anyone whose training has been heavily aerobic with little repetition work at pace, often see the opposite — the trick underestimates how tough their marathon day will feel relative to their 800m fitness.
Part of the problem is structural: the method compresses everything about marathon readiness — aerobic endurance, fuelling, pacing discipline, heat tolerance, and how well your body handles running for three-plus hours — into a single number derived from a workout that lasts about an hour. A more evidence-based approach is to use an actual recent race result and a distance-based formula, such as the Riegel formula used in our Race Time Predictor Calculator, which has been documented in sports-science literature and grounds its prediction in your own real race performance rather than a mnemonic. If you have run a recent 10K, 15K or half marathon, that calculator will generally give you a more defensible marathon estimate than a single Yasso 800 session will. Treat Yasso 800s as a fun, motivating benchmark workout — not as the number you build your race-day pacing plan around.
None of the above should be read as "don't bother with Yasso 800s." Strip away the prediction claim entirely, and what is left is a genuinely well-regarded marathon-specific training session: ten repeats of 800m at a hard, controlled effort, with recovery jogs that keep the overall session honest rather than turning it into an all-out sprint set. This kind of session builds your ability to hold a firm pace under accumulating fatigue, sharpens your leg turnover and running economy, and gives you a concrete, repeatable benchmark to track fitness changes over a training block — even if the specific marathon time it "predicts" should be taken with a grain of salt. Many marathon training plans, regardless of what they call the workout or whether they reference Yasso by name, include some version of 800m-to-1600m repeats at or near goal race pace for exactly these reasons. Do the workout for the training benefit first, and treat the marathon-time number it spits out as a bit of fun on the side.
Who invented the Yasso 800s?
Bart Yasso, longtime "Chief Running Officer" at Runner's World magazine, is credited with popularising the workout and the associated time-prediction trick. He has described noticing the pattern through his own training rather than through formal research, and it spread through the running community by word of mouth before becoming a widely referenced piece of marathon training folklore.
Is the Yasso 800 prediction actually accurate?
It is a popular rule of thumb, not a scientifically validated formula. It tends to land in a plausible range for some mid-pack marathoners with a fairly typical mix of speed and endurance training, but it is generally unreliable for very fast or very slow runners, and it does not account for real differences in aerobic base, fuelling, or pacing. Treat the number it produces as a rough, fun benchmark rather than a firm race-day target.
How do I build up to running 10 × 800m?
Start with fewer repeats — four to six — at a controlled, comfortably hard effort with full recovery jogs, and add one or two repeats every couple of weeks as your fitness and confidence improve. Most marathon plans place a session like this a few weeks out from race day, once a solid aerobic base has already been built, rather than as an early-training-block workout.
What pace should my recovery jog be?
An easy, conversational jog is the standard approach — the goal is to bring your heart rate down enough to attack the next 800m with good form, not to add extra training stress. The classic Yasso structure uses a recovery jog that takes roughly the same amount of time as the 800m rep itself, but the exact pace of that jog matters far less than keeping it genuinely easy.
Can beginners use Yasso 800s to predict a marathon time?
Beginners can run the workout, but should be especially cautious about trusting the number it predicts. Runners early in their training typically have a less developed aerobic base relative to their raw speed, which is exactly the scenario where this rule of thumb tends to be least reliable. A recent race result run through a distance-based calculator is usually a sounder guide for a first marathon goal.
How is the Yasso 800 different from the Race Time Predictor Calculator?
The Race Time Predictor Calculator uses the Riegel formula, a documented mathematical relationship between race distance and finish time, applied to an actual result you have run. The Yasso 800 method uses no such formula — it simply reinterprets the digits of a workout average as a marathon time. The Riegel-based approach is generally regarded as the more scientifically grounded of the two.
How often should I include a Yasso 800 session in marathon training?
Most plans that use this workout schedule it sparingly — every few weeks during the speed-focused phase of marathon training, not as a weekly staple. It is a demanding session, and its main value is as a fitness benchmark and pace-under-fatigue workout, so it works best alongside, not instead of, your long runs and easy aerobic mileage.