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Duathlon Calculator

Estimates duathlon finish time and run-bike-run splits from target paces.

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How to use this calculator

Templates are illustrative distances you can edit, not event regulations.

Run 15 km
:
T1
:
Bike20 km
T2
:
Run 22.5 km
:

Result

Enter a pace or speed for each leg to see your finish time and splits.

Constant average pace for each leg: no drafting, gradient or fatigue model. Estimate only — real results depend on course, weather, terrain, fatigue, transitions, equipment, nutrition and event rules. Not medical or coaching advice.

How the method works

Run → transition → bike → transition → run plan
Illustrative method
Run → transition → bike → transition → run planProportional five-segment time bar of a duathlon: 5 km run, transition, 20 km bike, transition, 2.5 km run, with each segment's time and the cumulative clock.Start 0:00Finish 1:20:1513525:001:04:301Run 1 · 5 km @ 5:00 /km25:002T1 · transition2:003Bike · 20 km @ 32 km/h37:304T2 · transition2:005Run 2 · 2.5 km @ 5:30 /km13:45Total (sum of every leg and transition)1:20:15
Run 1 25:00 + T1 2:00 + Bike 37:30 + T2 2:00 + Run 2 13:45 = 1:20:15 total.

Both transitions count toward the finish; with zero transitions the same plan is 1:16:15. Fixed example values for illustration — not your result.

Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.

How to use this calculator

  1. Pick Sprint or Standard and tick Edit distances to change them.
  2. Choose Metric or Imperial, then enter Run 1 pace, bike speed, Run 2 pace and the T1/T2 transitions (blank uses the default).
  3. Read the splits, cumulative times and finish clock (add a start time — a finish after midnight shows +1 day), the what-if card, save plans A and B to compare, and print a one-page race card.

How it works

Total = Run 1 + T1 + bike + T2 + Run 2, each run being distance ÷ pace basis × pace and the bike distance ÷ speed.

The what-if card is arithmetic on your own numbers: it shows which leg saves most time if it is 5% faster. It is not a prediction of fatigue.

Blank paces are missing, not zero; seconds must be below 60.

Worked example

Sprint duathlon. 5 km @ 5:00/km (25:00) + T1 2:00 + 20 km @ 32 km/h (37:30) + T2 2:00 + 2.5 km @ 5:30/km (13:45) = 1:20:15; with no transition time, 1:16:15. 5% faster on the bike saves the most (1:47).

Tips

  • Times are estimates only — not medical or coaching advice. Always train safely and follow event rules.
  • Distances are editable: choose “Custom…” to enter your own course lengths.

Frequently asked questions

What are typical duathlon distances?

Sprint ≈ 5 km run / 20 km bike / 2.5 km run; Standard ≈ 10 km run / 40 km bike / 5 km run. Courses vary, so distances are editable.

How accurate are these times?

They're estimates. Real race times depend on terrain, weather, elevation, fatigue, transitions, nutrition, equipment, drafting and water conditions. Use them for planning and pacing, not as a guarantee.

Do my inputs get uploaded?

No. Everything is calculated in your browser — nothing is sent to a server or stored.

What is Target Finish mode?

Enter a goal finish time and the paces/speeds for the other legs, then pick the leg to ‘solve for’. The calculator works out the pace or speed you'd need on that leg to hit your goal.

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Cite this tool

Zerdly. (2026). Duathlon Calculator. Retrieved from https://www.zerdly.com/tools/duathlon-calculator/

Tip: Enter any known values to calculate the remaining results.

Designed to run locally in your browser. Tool inputs are not intentionally stored by Zerdly unless stated otherwise.