Duathlon looks simple because there is no swim, but the opening run changes everything. If you treat the first run like a standalone race, the bike and second run usually fall apart.
A good duathlon plan keeps the first run controlled, rides steadily, and saves enough for the second run. Use the duathlon calculator to model run-bike-run splits and both transitions before race day.
Why the first run is the trap
The first run feels fresh, crowded, and exciting. That makes it easy to run 5K or 10K too hard. Even a small overpace can raise heart rate, burn carbohydrates, and make the bike feel harder than planned.
Sprint duathlon example
A common sprint format is 5 km run, 20 km bike, and 2.5 km run. A balanced plan might use a controlled first 5K, a bike speed you can sustain without surges, and a second run pace 10-30 seconds per km slower than the first run.
Transitions still matter
Duathlon transitions are quick, but they still count. Practice shoes, helmet, bike mount, and dismount flow. Saving one minute in transition may be easier than forcing another minute from the final run.
How to estimate your finish time
Enter the first run pace, bike speed, second run pace, T1, and T2. If the second run looks unrealistic, slow the first run or reduce the bike target until the full race plan is balanced.