How the calculator works
The calculator implements the equations Jack Daniels and Jimmy Gilbert published for converting race performances into training intensities. Two formulas do the work. The first estimates the oxygen cost of running at a given velocity. The second estimates the fraction of aerobic capacity a runner can sustain for a race of a given duration. Dividing one by the other turns your race result into a single fitness score, an effective VO2max, which is the number Daniels calls VDOT in his book Daniels' Running Formula.
Everything else on this page is that score run in reverse. To predict an equivalent race time, the calculator asks: what finish time at this other distance would imply exactly the same score? It solves that question numerically for each distance from 1500m to the marathon. To set training paces, it finds the velocity that corresponds to each published training intensity and formats the result as pace per mile or per kilometer.
What your score means
The score is the same fitness metric Daniels calls VDOT in Daniels' Running Formula. It is more useful than a lab-measured VO2max because it bakes in your running economy: two runners with identical lab values but different mechanics will race at different speeds, and the race-derived score reflects that. It is a single number that summarizes what you can actually do on a course, which makes it the cleanest way to track fitness across a season. Recreational runners typically score in the 30s and 40s, strong club runners in the 50s and 60s, and elites in the 70s and 80s. A one-point gain is roughly 10 to 15 seconds off a 5K, so climbing two or three points over a training block is real, visible progress.
Equivalent times vs the Riegel prediction
Our race time predictor answers a similar question with a different model. Riegel's formula is a single power law: pace decays a fixed percentage every time distance doubles, with an exponent you pick. The equivalency table here instead converts your race to a fitness score and solves each distance from the physiological drop-off curve. In the middle distances the two agree remarkably well: a 19:57 5K maps to about a 3:10:48 marathon here and about 3:11:20 under Riegel at 1.06.
The divergence is at the edges, and it tells you which tool to reach for. Riegel's adjustable exponent is a feature when you are stepping up to a marathon on modest mileage: raise it to 1.08 or 1.10 and the prediction stops flattering you. The score-based model assumes you are equally trained for every distance it prints, which is the right assumption for setting workout paces and comparing performances, and the wrong one for a first marathon off 30 miles per week. Use this page to anchor training and judge which of your results was strongest; use the predictor when you want an honest goal for a distance you have not trained for yet.
The five training paces
- Easy spans 59 to 74 percent of your effective VO2max. This is conversation pace, and it should account for most of your weekly mileage.
- Marathon pace comes from solving the race equations for the full 26.2-mile distance at your current fitness, so the calculator also shows your projected marathon time.
- Threshold sits at 88 percent: comfortably hard, sustainable for 20 to 40 minutes as a tempo run or broken into cruise intervals.
- Interval pace is 100 percent of your effective VO2max, run as hard repeats of 3 to 5 minutes. The calculator shows a per-400m time for track sessions.
- Repetition pace is 105 percent: short, fast reps with full recovery that build speed and running economy rather than aerobic fitness.
Worked example: a 19:57 5K
Say you just ran a 19:57 5K. Enter 5K and 19:57, and the calculator returns a fitness score of 50.0. The equivalency table then reads out what that same engine predicts elsewhere: a 5:50 mile, a 41:21 10K, a 1:31:35 half marathon, and a 3:10:48 marathon. From the same score it derives an easy range of 7:52 to 9:26 per mile, marathon pace of 7:16, threshold pace of 6:51, interval pace of 6:10 (about 92 seconds per 400m), and repetition pace of 5:56 (about 89 seconds per 400m). Notice the spread: three and a half minutes per mile separates a recovery jog from a repetition. Runners who train without these anchors tend to compress everything into the middle, too fast on easy days and too slow on hard ones, which is the surest way to plateau.
Which race result to use
Use a recent, all-out race between 5K and half marathon for the best results. Those distances are long enough to be genuinely aerobic and short enough that pacing errors and fueling problems rarely distort the time. A mile works too if it was a true race effort. Ultramarathons do not: aid stops, terrain, and fueling dominate ultra finish times, so the equations cannot read your aerobic fitness from them. Time trials are acceptable if you honestly emptied the tank, though most runners go a bit faster with competition and a finish line. Recalculate after each new race, or after every 6 to 8 weeks of consistent training, so your paces keep pace with your fitness instead of anchoring you to who you were last season.
Score reference table
The table below maps whole-number scores from 30 to 85 to representative race times at the four most common distances, computed from the same equations as the calculator. Find your recent time in a column to read your approximate score, or look one or two rows down to see what the next fitness level buys you. Copy it into a spreadsheet or print this page to keep it on the fridge.