English Endurance
Triathlon Performance Calculator
Discipline-specific training zones and race split predictions for Olympic, 70.3, and Ironman triathlon. Enter threshold values for each sport, or use the Race Predictor to model performance from a total finish time.
Zone spectrum — % of CSS speed
Training zones
| Zone | % of CSS | Pace / 100m | Description |
|---|
Triathlon swim splits
| Distance | % of CSS | Pace range / 100m | Predicted split |
|---|
Critical Swim Speed (CSS) is the aerobic swim threshold — the fastest pace sustainable for extended continuous effort, analogous to LT2 for running. Determined by a 400m and 200m time trial: CSS = (400m − 200m distance) ÷ (400m − 200m time). Paces shown apply to open-water wetsuit swims; pool swims are typically 2–6 sec/100m faster. Olympic swims are close to or slightly above CSS; Ironman swims are well below due to distance, pacing strategy, and pre-race energy conservation.
Zone spectrum — % of threshold speed
Training zones
| Zone | % of threshold | Speed (mph) | Description |
|---|
Triathlon bike splits
| Distance | % of threshold | Speed range | Predicted split |
|---|
Threshold speed represents your FTP-equivalent average on flat terrain in still air — use it as a training reference, not a race target. Triathlon bike targets are set conservatively below FTP to protect run performance: Olympic athletes can push close to threshold; 70.3 targets 87–95%; Ironman typically 75–83%. Actual speeds vary substantially with elevation, wind, and equipment. Power-based pacing remains more reliable for race execution.
Zone spectrum — % of threshold speed
Training zones
| Zone | % of threshold | Pace / mile | Description |
|---|
Triathlon run splits (fatigue-adjusted vs. standalone threshold)
| Leg | % of standalone threshold | Pace range / mile | Predicted split |
|---|
Triathlon run paces are expressed as a percentage of standalone run threshold speed, accounting for swim and bike fatigue. Olympic runs are close to standalone 10k effort (minimal fatigue). 70.3 runs are 10–20% slower than a fresh half marathon. Ironman runs are 20–32% slower than a fresh marathon — glycogen depletion, heat, and accumulated muscular fatigue compound significantly. Athlete-specific swim-to-bike-to-run fitness balance can shift these ranges substantially.
Split breakdown
Estimated splits & implied thresholds
| Segment | Distance | Est. split | Avg pace / speed | Implied threshold |
|---|