The half marathon is one of the most deceptive distances in running. At 13.1 miles it is long enough to punish poor pacing severely, but short enough that it feels manageable on race morning. The result is a distance with a specific and common mistake: starting too fast and paying for it between miles 9 and 13.
Good half marathon performance begins weeks before race day, with training at the right intensities — and it begins in the first mile with the right race pace. Both require knowing your numbers.
What Determines Your Half Marathon Race Pace
Your ideal half marathon race pace is not a guess or an aspiration. It is a function of your current aerobic fitness — specifically, your VDOT score — combined with the specific physiological demands of the 13.1 mile distance.
The half marathon sits at the upper end of what exercise physiologists call the lactate threshold zone. A well-trained runner racing a half marathon is working at or slightly above their lactate threshold for the entire event — roughly 88 to 92 percent of VO2max for most runners. This means half marathon pace is somewhat faster than traditional Threshold training pace but slower than 10K race pace.
The practical implication: your half marathon race pace is predictable from any recent race performance at a shorter distance. A solid 5K or 10K result gives you all the information needed to project your half marathon potential and calibrate your training accordingly.
Using the Calculator to Find Your Half Marathon Pace
Enter your most recent 5K or 10K time into the Age Graded Running calculator with the Half Marathon distance selected. The calculator derives your VDOT score and returns your half marathon-specific training zones along with your projected race pace.
A few notes on getting the most accurate result:
Use a recent, well-executed race on a flat course. A 5K run in ideal conditions three weeks ago is more useful than a 10K from eight months ago in heat. The calculator is only as accurate as the input.
If you have a recent half marathon time, use that directly for the most precise zone calibration. The calculator will derive your VDOT from your actual half marathon performance and return training paces tuned to that specific fitness level.
Your VDOT score and training zones should be updated every 8 to 12 weeks as fitness changes, or after any significant race.
The Training Foundation: Threshold Work
More than any other distance, the half marathon is a threshold event. Raising your lactate threshold — the pace at which lactic acid accumulates faster than it can be cleared — is the highest-leverage training investment available for half marathon performance.
Threshold training takes two main forms. Tempo runs of 20 to 30 continuous minutes at Threshold pace (slightly slower than 10K race pace, harder than a comfortable long run) build the sustained threshold fitness needed for 13.1 miles. Cruise intervals — typically 4 to 6 repetitions of 1 mile at Threshold pace with 60 to 90 seconds of recovery — allow more total volume at threshold intensity with slightly lower fatigue cost.
One threshold session per week, consistently executed over 12 to 16 weeks, produces substantial improvements in half marathon performance for most runners.
Long Runs and the Aerobic Foundation
The aerobic base determines your ceiling for half marathon performance. Long runs — typically 10 to 15 miles for half marathon training — build the mitochondrial density, capillary development, and fat oxidation capacity that make the later miles of a half marathon manageable.
Most long runs should be at Easy pace — genuinely conversational, roughly 60 to 90 seconds per mile slower than your projected half marathon race pace. The temptation to push long runs harder is real, particularly as race day approaches, but the aerobic stimulus of easy long running is substantial on its own and the recovery cost is much lower than pushing the pace.
In the final 6 to 8 weeks of a half marathon training block, incorporating the final 3 to 4 miles of some long runs at Marathon pace (slightly slower than half marathon race pace) adds a useful stimulus without the recovery cost of full threshold work.
A 16-Week Training Structure
A practical 16-week half marathon training framework for a runner with a solid base (at least 25 miles per week comfortably) distributes training roughly as follows:
Weeks 1 to 4 (base building): Establish weekly mileage at target level, all running at Easy pace except one threshold session per week. Focus on consistency and aerobic base.
Weeks 5 to 10 (threshold development): One threshold session weekly (alternating tempo runs and cruise intervals). One moderate interval session every 10 to 14 days. Long run building to 12 to 13 miles at Easy pace.
Weeks 11 to 14 (race-specific work): Threshold sessions continue. Long runs incorporate Marathon-pace segments in final miles. One tune-up race of 5K or 10K to recalibrate VDOT.
Weeks 15 to 16 (taper): Reduce mileage by 25 to 40 percent. Maintain one short threshold session. Arrive at the start line rested and sharp.
Pacing Your Half Marathon Race
The most useful output from the calculator for race day is your projected half marathon pace. This becomes your target for the first half of the race — not a pace you fight to maintain, but a pace that feels controlled and sustainable.
The common mistake is treating half marathon pace as the floor rather than the ceiling in the early miles. Running the first 5K even 15 to 20 seconds per mile faster than target pace creates a metabolic debt that compounds over the back half of the race. The runners who finish half marathons strongly are nearly always the ones who felt slightly held back in the first 5 miles.
A practical pacing approach: target your calculated race pace for miles 1 through 8, allow yourself to respond to how you feel from mile 8 to 10, and race the final 5K. If you have paced the first two thirds correctly, you will have something left for the finish.
Age-Grading Your Half Marathon
For masters runners, the calculator adds a dimension that raw times cannot provide: your WMA age-grade score for the half marathon.
Because the half marathon sits within a narrow performance window — the event separates runners more finely than the 5K but less than the marathon — age-grade scores for the half tend to be particularly meaningful indicators of overall running fitness.
A 58-year-old male running a 1:55:00 half marathon has an age-grade score of approximately 68 percent — solidly in the Local Class tier. The open equivalent time for that performance is approximately 1:27:00, meaning a 25 to 34-year-old at the same relative fitness level would be targeting a 1:27 half. That context transforms what the raw 1:55 means.
For masters runners tracking fitness across a training season, the half marathon age-grade score is one of the most informative single data points available. It is long enough to reflect genuine aerobic fitness (unlike the mile, which heavily rewards speed), short enough to race frequently (unlike the marathon), and benchmarked against a well-developed WMA standard.
A Note on the Calculator’s Half Marathon Age-Grade
The Age Graded Running calculator uses 5K road age factors as an approximation for half marathon age-grading, since distance-specific WMA half marathon tables were not embedded in the current version. For most practical purposes — tracking fitness trends, comparing performances across training cycles — this approximation is accurate. For official competitive age-grading at masters events, consult the full WMA tables at worldathletics.org.