Half Marathon Time Predictor

Predict 13.1 mi via Riegel.

Inputs

Result

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How to use this calculator

  • Recent race + time.
  • Read prediction.

About this calculator

13.1 mile half marathon predictor. From 10K: most accurate. From 5K: optimistic. From full marathon: conservative. Train with progressively longer runs (peak at 11-13 mi long run) for best half-marathon performance. Most amateur halves: 1:45-2:30. Sub-2:00 is a common amateur goal — equates to ~9:09/mi pace.

Frequently asked

Long run training?+
Peak long run: 10-12 mi for half marathon (don't need to do 13 in training). Shorter runs build base.
Sub-2 pace?+
~9:09/mi. Sub 1:45: ~8:00/mi. Sub 1:30: ~6:52/mi (competitive).
Hill effect?+
+1.5-3% time per 100ft elevation gain. Match prediction to course profile.
Wall in halfs?+
Less common than full marathon — body has glycogen for ~17-20 mi at race pace. Dehydration is bigger risk.
Pacing strategy?+
Even or slight negative split. Going out 10s/mi too fast in first 5K can cost 30-60s by mile 13.

Related calculators

5K Time Predictor (Riegel)
Predict 5K from another race using Riegel formula: T₂ = T₁ × (D₂/D₁)^1.06.
10K Time Predictor (Riegel)
Predict 10K via Riegel: T₂ = T₁ × (D₂/D₁)^1.06.
Marathon Time Predictor
26.2 mi via Riegel. Most accurate from a recent half marathon.
Race Time Predictor (Riegel formula)
Predict your time at any distance using Riegel's formula T₂ = T₁ × (D₂/D₁)^1.06.
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VO2max ≈ (distance in meters − 504.9) / 44.73. Cooper test estimates aerobic fitness.
Lactate Threshold Pace Estimator
LT pace ≈ pace you can hold for 60 min. Estimate from recent race or HR zone.

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