Enter sustainable training paces for each discipline and we'll model realistic swim, bike, and run splits plus transitions. Toggle between metric and imperial (US) units. Numbers update live.
Our 24-week Half Ironman program is built by an RRCA/USAT-certified coach and used by athletes targeting sub-5h and sub-4:30 70.3 finishes.
Predict your full Ironman 140.6 finish — 3.8 / 180 / 42.2 km with transitions.
Open Full Ironman PredictorSister calculator for the full IM distance — bike & run fade modeled.
Carbs/hr, sodium and fluids — personalized for your 70.3 split.
Race-week carb load to protect the predicted run pace.
Bottle-by-bottle hydration plan for the 70.3 bike and run.
Breno MeloHead Coach · USA Triathlon, Road Runners Club of America, TrainingPeaksYour predicted 1.9 / 90 / 21.1 splits, transitions and target paces on one printable card.
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Swim 1.9 km from CSS; bike 90 km from FTP and an assumed intensity factor of 0.78–0.83; run 21.1 km from VDOT half-marathon pace de-rated for accumulated bike load; plus transitions.
Not externally validated. Component models (VDOT, FTP, CSS) are cited; the assembly is this practice's own.
Formula, constants and cited sources last verified on . Spotted something wrong? Email breno@brenoamelo.com and it gets corrected and dated.
Each leg is predicted from a standalone benchmark, then adjusted for the fatigue the previous leg leaves behind.
The run carries the largest correction: most age-groupers run 30-75 seconds per mile slower off the bike than in a standalone half.
Transitions default to realistic age-group times rather than professional ones.
Every physiological claim on this page traces to one of the primary sources below — the original paper, textbook or governing-body standard, not a secondary write-up.
Copy a formatted reference below. If you are quoting a number from this page, please link back to it so readers can check the source and the date it was last reviewed.
Breno Melo, "Half Ironman 70.3 Time Predictor — Breno Melo Endurance Coaching", Breno Melo Endurance Coaching (last reviewed 18 May 2026). https://www.brenoamelo.com/calculators/half-ironman-time-predictor
Within roughly 5-8% if you input race-realistic paces: swim CSS, sustainable bike speed or power, and open half-marathon pace plus 15-30 seconds per kilometre for accumulated fatigue.
1.9 km (1.2 mi) swim, 90 km (56 mi) bike and 21.1 km (13.1 mi) run - 70.3 miles in total.
Age-group athletes typically take 3-5 minutes for T1 including the wetsuit strip, and 2-3 minutes for T2. The default here is 4 minutes T1 plus 2.5 minutes T2.
Sub-6 hours is a solid age-group result, sub-5 hours is competitive, and podium times in most age groups sit between 4:20 and 4:50 depending on the course.
Around 75-82% of FTP as normalized power for most age-groupers. Riding above that range reliably costs more time on the run than it saves on the bike.
Considerably. A hilly bike course with 1,200 m of climbing can add 15-25 minutes over a flat one at the same power, and it raises the run penalty too.
How standalone splits translate to a race-day 70.3 clock.
Bottle-by-bottle fueling for four hours and up.
Carbs per hour, gel timing and the gut training that makes it work.
Two sessions a week that protect your durability.
A 70.3 prediction assumes you can run off a 90 km bike. Apex builds the bricks, long rides and fueling rehearsals that make the assumption true.
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1:1 coaching builds the 16-24 week block, the race-week plan, and the pacing strategy that gets your predicted time onto the clock.
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