How accurate is a Half Ironman 70.3 time predictor?

Within ~5–8% if you input race-realistic paces — swim CSS, bike sustainable power/speed, and run open-half-marathon pace plus 15–30 seconds per kilometer for accumulated fatigue.

What are the Half Ironman 70.3 distances?

1.9 km (1.2 mi) swim, 90 km (56 mi) bike, and 21.1 km (13.1 mi) run — 70.3 miles total.

How long do transitions take in a 70.3?

Age-group athletes typically take 3–5 minutes for T1 (wetsuit strip + bike out) and 2–3 minutes for T2. The default here is 4 min T1 + 2.5 min T2.

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Breno Melo

70.3 / Half Ironman Predictor

Predict your Half Ironman 70.3 finish time.

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.

Units

Swim pace (mm:ss / 100m)Bike speed (km/h)Run pace (mm:ss / km)T1 (min)T2 (min)

Race-day conditions

Course profile

Temperature

Humidity

Predicted 70.3 finish

5:15:35

Swim 1.9 km

34:50

4:00

Bike 90 km

2:48:45

2:30

Run 21.1 km

1:45:30

How to enter race-realistic paces

Swim: use your CSS pace (Critical Swim Speed), not 100m max effort.
Bike: the speed you can hold at ~75–80% of FTP for 2h30 on race terrain.
Run: open half-marathon pace + 15–30 sec/km (or +24–48 sec/mi) for off-the-bike fatigue.

Want a full 24-week 70.3 plan?

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.

Going full distance?

Predict your full Ironman 140.6 finish — 3.8 / 180 / 42.2 km with transitions.

Open Full Ironman Predictor

Related calculators

Full Ironman time predictor

Sister calculator for the full IM distance — bike & run fade modeled.

AI race-day nutrition plan

Carbs/hr, sodium and fluids — personalized for your 70.3 split.

Carb loading calculator

Race-week carb load to protect the predicted run pace.

Sweat & sodium calculator

Bottle-by-bottle hydration plan for the 70.3 bike and run.

Want a coach to apply this?

IRONMAN 70.3 coach

1:1 coaching specifically for the 70.3 distance.

Triathlon coach

Sprint to full IRONMAN — fully custom 1:1.

Online triathlon coach

Remote 1:1 coaching for triathletes worldwide.

First triathlon coach

Beginner-friendly programming with open-water focus.

From the coach

A 70.3 prediction is one thing. Executing it is another.

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.

Apply for 1:1 coaching Book a free 20-min call

Boston-based · Trilingual EN/PT/ES · RRCA · USAT · TrainingPeaks L2 · 12× Boston qualifier