Race time predictor and training paces

What this race time predictor does

Type in your VO₂ max, or a race you ran recently, and the tool gives you two things: predicted times for 5K, 10K, half marathon and marathon, and five training paces you can use straight away. It is built on the formulas Jack Daniels and Jimmy Gilbert published in 1979, which link running speed, oxygen use and how long you can keep up a given effort. Those same formulas sit behind the "VDOT" tables many runners know from Daniels' Running Formula.

How to use it

1. Pick your starting point. A recent race is the best input, because it already includes your running economy, pacing and toughness. Use a race from the last six to eight weeks, run flat-out on a fairly flat course.
2. Or enter a VO₂ max. If you have a lab test or a field test from our VO₂ max calculator, enter that. Expect the predictions to be optimistic if you are not a regular runner (see limits below).
3. Read the times as "what is possible if trained". A 10K result predicts a marathon only if you have also done the long runs.
4. Use the paces for one to two months, then test again. When a new race or test comes in faster, update the numbers.

The five training paces

• Easy is the bulk of your running. If you can't talk in full sentences, slow down.
• Marathon pace is steady and controlled, useful at the end of long runs.
• Threshold is "comfortably hard", roughly what you could hold in a race of about an hour.
• Interval pace is close to the speed where you reach your VO₂ max, so reps of three to five minutes at this pace are the main way to raise it. Our Norwegian 4×4 workout is a classic example, and the free 8-week VO₂ max training plan builds these sessions in week by week.
• Repetition is faster still, in short reps with full rest, for speed and form.

The human side: why your number isn't your race

Two runners with the same lab VO₂ max can finish a 10K minutes apart. One has run for years and wastes little energy per stride. The other came from cycling and is new to running. The formulas can't see that difference when you enter a VO₂ max, but they can when you enter a race, because the race already shows how you use your engine. That is why we suggest a race first. And a bad day happens to everyone: a hot morning, a hilly course or a cold coming on will all give you slower paces than you are really capable of. If a result feels wrong, trust your best recent effort, not your worst.

Limits, in plain words

• It assumes you are trained for the distance. Speed from short races does not turn into marathon endurance on its own.
• It knows nothing about the course or weather. Hills, heat, wind and altitude all slow you down.
• Lab VO₂ max is not race fitness. Running economy and how much of your VO₂ max you can hold vary from person to person. Entering a VO₂ max usually predicts faster times than you will run, especially if you are not a regular runner.
• Age, sex and weight are not inputs. The formulas only use speed and time; those factors are already part of your race result.
• It is an estimate for training, not a medical test.

Tips for better predictions

• Use a race, not a training run or a watch estimate.
• Pick the race closest to your goal distance.
• Make sure the course was the right length; GPS often reads a little long or short.
• Retest every six to eight weeks rather than chasing faster paces every week.

Related: VO₂ max calculator · heart-rate zones · Norwegian 4×4 builder · 8-week training plan

FAQ

How accurate is the race time predictor?

For a runner who is trained for the distance, the predictions are usually close. They get less reliable the further your goal is from the race you entered, and when you start from a VO₂ max instead of a race.

Is this the same as a VDOT calculator?

It uses the same published Daniels & Gilbert formulas, so the numbers are very close to VDOT tables. VDOT is a trademarked name, so we call our number a running fitness score.

Why is my marathon prediction too fast?

The marathon depends on endurance and fuelling, not only fitness. If you haven't done long runs of 25–32 km, expect to be slower than the prediction.

Should I use my watch's VO₂ max?

You can, but watch values are estimates and can be off by several points. A recent race gives better results.

How often should I update my paces?

Every six to eight weeks, or after a new race or test.

Can I use it for walking or cycling?

No. The formulas describe running only.

Sources

1. Daniels J, Gilbert J. Oxygen Power: Performance Tables for Distance Runners. Tempe, AZ: self-published; 1979. Equations for oxygen cost of running and the fraction of VO₂ max held over time.
2. Daniels J. Daniels' Running Formula. Champaign, IL: Human Kinetics (3rd ed. 2014). Training-pace tables (easy, marathon, threshold, interval, repetition).

Last updated: October 23, 2026. Written with AI assistance; predicted times checked against published Daniels table values (within 10 seconds at scores 40, 50 and 60).