Running, cycling and hiking
Race Hydration Planner
Turn event logistics and personal context into a plan you can rehearse. The output prioritises ranges, aid-station access and overhydration safety instead of one fixed volume per mile.
Jump to the printable aid-station pocket card →
Endurance event strategy
Build a practical hydration plan
Match fluid opportunities to event duration, conditions, measured sweat rate and the aid stations or bottles you can actually use.
Example — adjust the details
21 KM · 2h 05m
Example plan
- StartDrink normally beforehand; avoid excessive last-minute drinking.
- 5.0 km150–300 ml, adjusted for thirst, comfort and conditions.
- 10 km150–300 ml, adjusted for thirst, comfort and conditions.
- 15 km150–300 ml, adjusted for thirst, comfort and conditions.
- 20 km150–300 ml, adjusted for thirst, comfort and conditions.
- FinishKeep 25–75 ml available for the final 1.1 km; then reassess thirst, symptoms and recovery time and recover gradually with normal food and fluid.
Electrolytes: Electrolytes become more relevant as duration, heat and sweat loss increase. Use the electrolyte calculator for context.
Safety: do not drink enough to gain body weight during the event. Headache, nausea, confusion and swelling can occur with exercise-associated hyponatraemia as well as other serious conditions. Stop and seek appropriate medical help for concerning symptoms.
Make a race pocket card
Use the organiser's confirmed station distances. This example assumes even pace; hills, queues and stops change arrival times. It does not assign a compulsory amount to drink.
What the race hydration planner calculates
The planner converts event distance and expected duration into elapsed time between fluid opportunities. If you supply a valid measured sweat rate, it uses a rounded 60–90% range below the measured loss rate. If you do not know it, the result stays deliberately broad and responds only to the visible heat and humidity settings.
Bottle capacity turns the total range into container equivalents. Aid-station spacing turns the hourly range into portions for each section of the route, including the final partial leg. Activity and electrolyte choices provide relevant labels and interpretation; they do not apply hidden physiological multipliers.
Worked example
A two-hour half marathon with a measured 0.8 L/hour sweat rate
The measured session suggests about 1.6 litres of sweat loss over two hours. The planner’s 60–90% starting range rounds to 475–725 ml/hour, or 950–1,450 ml across the event. That is approximately 1.9–2.9 × 500ml containers before considering what is actually available on the course.
This does not mean every runner should consume that range. Rehearse it in comparable conditions, remain below a level that produces body-mass gain, and reduce the plan when thirst, stomach comfort, pace or cooler weather indicates less.
How to use aid-station spacing
- Use the organiser’s current course map, not a remembered value from a previous year.
- Enter the distance between stations in the same unit as the event.
- Read each figure as the volume available for that leg, not an instruction to empty a full cup.
- Check the final partial leg and decide whether you need to carry a reserve.
Start with a representative sweat-rate test, then use the bottle planner when your event relies on carried containers rather than aid stations.