Recently I floated the value of using an 8K as a marathon time predictor shortly before your marathon, in lieu of the popular Yasso 800’s workout.

While the 8K/10 can cut out a middleman and give you the same result as the Yasso’s, possibly more accurate since the breaks are removed… as I mentioned, it can be difficult to find an 8K to race.

I’ve done some more research based on Daniels’ pace recommendations, and I realize that a 5K may provide a similar prediction. This may work better for most people, because 5K races are a lot more common and easier to find, register for and complete.

Of course, the following assumes:

- You’re trained to run the marathon distance, and can comfortably run at least 2.5 uninterrupted hours.
- Your workouts haven’t been a substantial struggle to complete (aside from finding the time to do them, and making the proper effort to recover from those workouts)
- It also helps if you know your goal pace, though this is not necessary.

Basically, you simply run a 5K at your best sustainable effort for the 5K distance. Do not taper for this 5K, and do not plan for rest days afterward. This is not going to be a max effort 5K.

If you know your marathon goal time, a starting guideline is to aim to run the 5K about one minute per mile faster than your marathon goal pace. It doesn’t have to be exactly this, but if unsure how fast to run the 5K this is a fine starting point. And if that seems too fast for you… your marathon goal time might be too ambitious for a full 26.2, even if you’ve been able to hit it during marathon-pace workouts.

Either way, the best effort guideline for this race: **Run the 5K as if you have to also do a regular workout tomorrow**. You don’t want to take it too easy, but you don’t want to exhaust the tank to try and PR.

Running the 5K by feel honestly will produce the most accurate result. Run at a steady pace you can hold for 3 straight miles, and avoid the instinct to finish hard and kick at the end.

If at any point in the 5K you feel you can go faster, you may increase your pace *just a little bit*. But don’t exhaust yourself before the finish.

The harder the 5K is to run, the less likely you can hold for 26.2 the marathon pace it will predict. Your aerobic fitness is part of what’s being estimated, so it’s important this 5K be a challenging but otherwise aerobically comfortable effort.

Run the 5K. Once you have your 5K finish time, it’s time for some math.

**Step One:** Take your total time in raw minutes: Take the seconds, divide them by 60, and add that decimal to the whole number minutes.

For example, let’s say an aspiring marathoner who run 50 miles a week and has knocked out his/her 20 miler… subsequently ran the 5K in 24:24.

24 seconds is equal to 0.4 minutes, which added to 24 whole minutes makes 24.4.

## 24:24

## 24 seconds / 60 = 0.4 minutes

## 24 minutes + 0.4 minutes = 24.4 minutes.

**Step Two:** Now, multiply that number by 0.16.

## 24.4 x 0.16 = 3.90

This number is the number of estimated hours it should take you to finish the marathon.

**Step Three:** You can take the decimal in this hours estimate, and multiply that by 60 to display the number of minutes.

## 0.90 hours / 60 = 54 minutes

## 3.90 hours —-> 3 hours, 54 minutes

## 5K Marathon Prediction: 3 hours, 54 minutes

According to the 5K prediction, a trained marathoner who can knock out a 5K in 24:24 can likely run their marathon in 3 hours, 54 minutes.

If the above hypothetical marathoner were to run the Yasso 800’s, they likely could complete their 800 reps in an average of 3 minutes 54 seconds.

If they ran the 8K/10, it would take them roughly 39 minutes on the dot.

But the 5K can give them the same estimate, in a fraction of the time and effort. The only extra effort is in doing the math.