What Yasso 800s are
Yasso 800s are a marathon prediction workout popularized in the 1990s by Bart Yasso of Runner's World. The claim is simple: if you can run 10 x 800m on the track with each repeat at the same time in minutes and seconds as your marathon goal in hours and minutes, that goal is plausible. A runner chasing a 3:30 marathon runs ten 800s in 3 minutes 30 seconds each. Between repeats you jog for the same duration as the repeat itself, so the recovery is built into the test. The calculator above just swaps the units for you in either direction.
Why folk wisdom roughly works
There is no physiological law connecting 800m speed to marathon endurance, so why does the rule hold up as often as it does? Two reasons. First, your time for 10 x 800m with short recoveries is a decent proxy for overall fitness: it reflects speed, aerobic power, and the ability to repeat hard efforts. Second, the minutes-to-hours mapping happens to land close to what formal endurance models such as Riegel's formula predict for well-trained runners moving from middle-distance speed to the marathon. It is a coincidence of units, but a useful one, which is why coaches have kept the workout around for three decades.
Where it breaks
Be honest about what the workout measures. It says nothing about the endurance side of marathon fitness. Runners on low weekly mileage can hit every 800 on time and still blow up at mile 20, because glycogen depletion and musculoskeletal durability, not speed, are the marathon's real limiters. For many first-time marathoners the rule skews optimistic by 5 to 10 minutes, sometimes more if their long runs are thin. Treat Yasso 800s as a fitness check inside a real marathon block, with the long runs and weekly volume to back it up, not as a standalone prediction.
Worked example: chasing a 3:30 marathon
Say your goal is a 3:30 marathon. The Yasso prescription is 10 x 800m in 3:30 each, with a 3:30 jog between repeats. If you can complete the full set 2 to 3 weeks out from race day without the last two repeats falling apart, the rule says 3:30 is within reach. Going the other way, if you run a workout where your 800s average 3:00, the mapping points at a 3:00:00 marathon. Enter either number in the calculator and it returns the matching time on the other side.
Related tools and guides
For a prediction grounded in an actual race result, use the race time predictor, which projects your fitness across distances with endurance models rather than folklore. Once you have a marathon goal, the splits calculator turns it into a printable pace band, and the training pace calculator sets the easy, tempo, and interval paces for the rest of your block. Before race day, read the marathon pacing mistake that costs you the last 10K.
Frequently asked questions
How accurate are Yasso 800s as a marathon predictor?
Roughly accurate for well-trained runners on solid mileage, and optimistic by 5 to 10 minutes for many first-timers. The workout measures speed and repeatability, not the fueling and durability that decide the last 10K of a marathon. Treat the result as a fitness check inside a real marathon block, not a guarantee.
When in a marathon training block should I run Yasso 800s?
Run the full 10 x 800m session 2 to 3 weeks before race day, at the peak of your block. Earlier in the cycle, start with 4 to 6 repeats and add one every week or two so the full set arrives right when your taper begins.
What recovery should I take between the 800m repeats?
A jog of the same duration as the repeat itself. If your repeats take 3:30, jog easy for 3:30 between them. The equal-time jog recovery is part of the test; standing rest or shorter recoveries make the times faster than the rule assumes.
Can beginners use Yasso 800s?
Yes, as a workout, with caution as a predictor. Newer runners often have enough speed to hit the 800 times but not the aerobic base to hold the matching marathon pace for 26.2 miles, so the mapping skews optimistic for them. Build mileage first and use the session as a checkpoint, not a promise.
Do Yasso 800s work for the half marathon?
No. The minutes-to-hours mapping is marathon folklore specific to 26.2 miles; there is no equivalent Yasso rule for 13.1. For half marathon goals, use a race time predictor based on a recent race result instead.