Power-based bike prediction
Bike speed is solved from power rather than guessed from a generic average-speed table. Course gradients are modelled as segments, so extra body and bike weight matters more on climbing-heavy courses.
Triathlon Course Time Calculator
Estimate your finish time on a specific IRONMAN or IRONMAN 70.3 course using course profile, bike power, aerodynamics, equipment, running pace and swim pace.
Course-specific, not just pace × distance.
The model adjusts the bike for gradients, weight, CdA, rolling resistance, wind exposure and technical time loss; the run for elevation, turns and course friction; and the swim for water conditions plus route geometry. Official/map-derived geometry is used when available; otherwise a conservative source-tagged model is down-weighted automatically.
1
Choose your race
Course data is loaded from the Triathlon Loop race database.
COURSE
—
—
—bike gain
—run gain
—bike terrain
—data quality
2
Course effect —
Swim
Enter the pace you could hold in calm, open-water conditions.
SELECTED COURSE · SWIM MODEL
How this swim course changes your pace
—
Water—
Layout—
Turns—
Turnarounds—
Waves / chop—
Current—
The model combines water exposure, route geometry, turns, turnarounds and current before applying your wetsuit assumption.
3
Course effect —
Bike
Power + aerodynamics + total system weight drive the bike estimate.
Advanced bike & weather settings
4
Course effect —
Run & transitions
Use the pace you could sustain for this triathlon distance on a perfectly flat course after the bike.
A course-specific triathlon time calculator
Most triathlon calculators simply add a swim split, bike split and run split. That is useful for basic planning, but it treats a flat course and a mountain course as if they were the same race. This calculator is built differently: it starts with your own ability and then adjusts the estimate for the selected course.
On the bike, the model uses a simplified physics engine. Your expected power must overcome aerodynamic drag, rolling resistance and gravity. The calculator also accounts for total system weight, approximate CdA, air density, drivetrain efficiency, wind exposure and time lost on technical sections. That is why the same 200 watts can produce very different average speeds at Copenhagen, Mallorca or another course.
Aerodynamics & equipment
Tri bikes, road bikes, rider position, helmet, wheels and clothing influence the model through an estimated CdA. If you know your measured CdA, use the advanced override for a better estimate.
Course profile
Bike and run calculations use course-specific grade distributions rather than elevation gain alone. Technical penalties can also represent tight turns, roundabouts and sections where speed must be reduced.
Uncertainty range
A single predicted time can look more precise than the data really is. The calculator therefore shows a sensitivity range based on course-data quality, weather uncertainty and whether your CdA is measured or estimated.
Why power, CdA and weight all matter on the bike
At higher speeds, aerodynamic drag becomes the dominant resistance. CdA—the product of drag coefficient and frontal area—is therefore one of the most important inputs on flat and fast courses. On steep climbs, gravity becomes more important and system weight matters much more. Rolling resistance and drivetrain loss contribute on every course.
BIKE MODEL
Power ≈ aerodynamic resistance + rolling resistance + gravity
The calculator solves speed iteratively for each representative course segment, then adds course-specific technical time loss.
Tools such as Best Bike Split and myWindsock use the same broad idea—combining power, course profile, aerodynamics, weather and rolling resistance—although their proprietary models and route datasets are much more detailed. Triathlon Loop's tool is designed as a transparent, free race-planning estimate rather than a replacement for professional modelling software.
How the run estimate is adjusted for hills
You enter the pace you believe you could sustain on a perfectly flat course after the bike. The calculator then applies a grade-adjusted energetic cost to the selected run course. Uphills cost more than equivalent downhills give back, so a hilly route normally produces a slower predicted time even when total ascent and descent are equal.
The underlying grade adjustment is inspired by established running-energy models and is applied segment by segment. A technical course can also include a small extra penalty for tight turns, mixed surfaces or other repeated interruptions.
How the swim estimate works
Swimming is harder to model from physics without individual drag and propulsion data, so the swim estimate starts with your realistic calm-water pace and then layers on course-specific friction. The model can account for the water type and typical wave/chop exposure, route layout and sighting demand, buoy-turn count, known current direction, and optional wetsuit benefit. When a race does not yet have detailed wave data, the calculator uses the database's water-type/course factor as a conservative fallback and increases the uncertainty range.
If your input comes from a pool, the model adds a small conversion penalty because pool pace benefits from walls and predictable navigation. Wetsuit benefit is user-selectable because research shows a meaningful but highly individual effect.
GET A BETTER ESTIMATE
Five inputs worth measuring before race day
- Your sustainable race power, not FTP. Use a number you can actually hold for 90 or 180 km while still running well.
- Your real system weight. Include bike, bottles, tools and race equipment—not only rider body weight.
- Your CdA if possible. Bike type alone cannot capture fit, position and rider size.
- A realistic post-bike run pace. Do not enter fresh 10K, half-marathon or marathon pace unless that is genuinely what you expect after cycling.
- Race-day wind. On exposed courses, wind can move the bike prediction by many minutes.
How accurate is the calculator?
The cycling portion can be physically well constrained when power, CdA, system weight, rolling resistance, route profile and weather are accurate. The largest uncertainties are usually aerodynamics, wind direction, braking and how an athlete distributes power over the course. Best Bike Split similarly highlights power, drag, weight, rolling resistance, weather and surface conditions as key race-time inputs.
Run and swim predictions should be treated more conservatively. Running response to hills varies between athletes, and open-water swim speed is influenced by navigation, drafting, waves, currents and crowding. The estimate is therefore best used for scenario planning: compare equipment, power targets and courses rather than treating one exact finish time as a promise.
Course time calculator questions
Can this estimate my bike speed from watts?
Yes. The bike model solves speed from expected average power, estimated CdA, total system weight, rolling resistance, gradients, air density and wind. It then adds course-specific technical time loss.
Why is bike type not enough to predict speed?
Two athletes on the same tri bike can have very different aerodynamic drag because body size and riding position dominate much of the frontal area. Bike type provides a useful starting preset, but measured CdA is more accurate.
Should I enter FTP as my bike power?
No. Enter the average power you realistically expect to produce over the race bike leg. For a 70.3 or full-distance triathlon, that will normally be below FTP.
Does the calculator include elevation gain?
Yes, but it does not use elevation gain as a single crude penalty. Each stored course can contain a representative distribution of uphill, flat and downhill segments so gravity is included directly in the bike model and grade-adjusted energy cost is used for the run.
Does wind affect the result?
Yes. You can enter expected wind speed. Course-specific wind exposure determines how strongly it affects the estimate. Because aerodynamic drag rises non-linearly, a headwind usually costs more time than an equal tailwind gives back.
Can I use a road bike instead of a tri bike?
Yes. Choose road bike, road bike with clip-on aerobars or triathlon/TT bike. The calculator changes the estimated CdA preset. You can override CdA entirely if you have better personal data.
How are corners and technical sections included?
Each race record can store a technical-time penalty representing repeated braking, sharp turns, roundabouts, narrow roads or other speed interruptions. Future versions can replace this summary penalty with route-level braking points from GPX data.
Will every IRONMAN and IRONMAN 70.3 be available?
The calculator is built for a global course database. Race data should be versioned and reviewed whenever an organiser changes a route. If a course is not yet in the database, it can be added without changing the calculator code.
What the model includes—and what it does not
| Discipline | Included | Not fully modelled |
|---|---|---|
| Swim | Distance, water type, typical wave/chop exposure, route layout, major turns, known current, pool/open-water source, wetsuit assumption | Pack drafting, minute-by-minute waves/current, individual swim drag and navigation error |
| Bike | Power, gradients, CdA, system weight, Crr, drivetrain, air density, wind exposure, technical loss | Exact yaw by metre, live traffic, rider-specific braking, drafting |
| Run | Baseline post-bike pace, grade-energy cost, surface factor, technical loss | Individual fatigue curve, exact heat physiology, aid-station behaviour |
Triathlon Loop calculator estimates are for planning and educational use. Course routes and organiser rules can change. Always verify the latest official athlete guide.