Run Your Next Marathon.

Enter a finish time and distance to get per-mile and per-kilometer splits. Generates cumulative split tables at every mile marker — useful for programming your watch or printing a pacing band. A 4-hour marathon works out to roughly 9:09/mi or 5:41/km.

Uses the Riegel formula (T2 = T1 × (D2/D1)^1.06) to extrapolate finish times across 5K, 10K, half marathon, marathon, and 50K. The 1.06 fatigue factor means doubling the distance costs more than double the time. Accurate within 2–3% for trained runners between 5K and marathon.

Uses the latest BAA qualifying standards (e.g. 3:00:00 for males 18–34, 3:30:00 for females 18–34) with age-group adjustments in 5-year increments. Factors in the cutoff buffer — recent years required beating your standard by 5–7 minutes for acceptance. Also flags times from courses with over 450m net elevation drop, which BAA rejects.

VDOT is Jack Daniels' metric that maps race performance to aerobic fitness while accounting for running economy. Calculates five zones: Easy, Marathon pace, Threshold (lactate turnpoint, ~60-minute sustain pace), Interval (VO2max efforts, ~12-minute sustain pace), and Repetition (speed/economy work). Recalculate after PRs or every 4–6 weeks.

Targets 40–60g carbs/hour for marathons (faster runners need the higher end due to higher glycogen burn). Plans hydration at 400–800ml/hour adjusted for heat. Your body stores roughly 2,000 calories of glycogen — about 90–120 minutes of hard running — so anything longer needs fueling. Includes carb-loading guidance at 8–12g per kg bodyweight for the 2–3 days before.

Scores six weighted factors: elevation gain per mile, max altitude (impact starts above 4,000ft), average grade, heat index, surface type, and course profile. Scale runs 10–30 (PR friendly), 31–55 (moderate), 56–75 (serious grind), 76–100 (brutal). Rule of thumb: every 100ft of elevation gain costs 12–15 seconds per mile.