Endurance Fuel Planner

Sport:

Pick Running or Cycling before setting carb, bottle, and sodium targets.

Duration:

Enter minutes of active running or riding, for example 120.

min

Intensity zone:

Use the zone that covers most of the session, not brief surges.

Carb target:

Enter grams per hour; many long sessions use 60-90 g/h.

g/h

Drink mix carbs:

Use prepared mix strength in g/L after dilution.

g/L

Bottle size:

Enter usable bottle volume, such as 500 or 750 mL.

Gel carbs:

Enter grams in one gel, chew serving, bar segment, or fuel unit.

Drink sodium:

Use prepared drink strength in mg/L after mixing.

mg/L

Gel sodium:

Enter mg per gel or serving; use 0 if it has no sodium.

Sodium profile:

Choose low, medium, high, or very high when no mg/L test is available.

Body weight:

Enter kilograms for estimated sweat loss; ignored when measured L/h is set.

Temperature:

Enter ambient temperature in C for the planned course conditions.

°C

Humidity:

Enter relative humidity from 0-100% for the route or race window.

Measured sweat rate:

Enter tested L/h from a sweat test; leave 0 to estimate.

L/h

Sweat sodium override:

Enter mg/L from a lab or field estimate; leave 0 to use profile.

mg/L

Salt cap dose:

Enter sodium per capsule or tablet, such as 200 mg.

Timeline interval:

Use 10-20 minutes for dense reminders, or longer for a compact table.

min

Metric	Value	Copy
Duration	{{ duration_hm }}
Carbs (g/h)	{{ carb_target_gph }}
Total carbs (g)	{{ Math.round(total_carb_g) }}
Fluid (L/h)	{{ fluid_lph_display }}
Total fluid (L)	{{ fluid_total_l_display }}
Drink concentration (g/L)	{{ Math.round(drink_carb_g_per_l) }}
Drink carbs (g/h)	{{ Math.round(drink_carb_gph) }}
Solids carbs (g/h)	{{ Math.round(solids_carb_gph) }}
Gels per hour	{{ gels_per_h_display }}
Bottles per hour	{{ bottles_per_h_display }}
Sodium target (mg/h)	{{ Math.round(sodium_target_mgh) }}
Sodium from drink (mg/h)	{{ Math.round(drink_sodium_mgh) }}
Sodium from gels (mg/h)	{{ Math.round(gel_sodium_mgh) }}
Sodium shortfall (mg/h)	{{ Math.round(sodium_shortfall_mgh) }}
Salt caps per hour	{{ salt_caps_per_h_display }}
Totals: gels / bottles	{{ gels_total_display }} · {{ bottles_total_display }}

#	Window	Carbs (g)	Drink (mL)	Sodium (mg)	Copy
{{ r.idx }}	{{ r.time }}	{{ r.carb_g }}	{{ r.drink_ml }}	{{ r.sodium_mg }}
No fueling windows yet Enter a positive duration and interval to build the timeline table.

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Long runs and rides turn food and drink into a pacing problem. Once a session lasts long enough to drain stored carbohydrate, raise sweat losses, or make aid-station access uncertain, a good plan has to answer more than what to carry. It has to say how much carbohydrate is coming each hour, how much fluid is realistic to drink, how sodium will be replaced, and how those targets will be split into repeatable windows while effort is still high.

Endurance fuel is usually planned as a rate, not only as a total. A three hour ride at 80 g of carbohydrate per hour needs 240 g overall, but the more practical question is how those grams arrive without stomach overload. Some can come from drink mix, some from gels, chews, bars, or real food, and the split matters because high drink concentration, warm weather, and hard running can all make absorption harder. The same logic applies to fluid and sodium. A bottle count that looks manageable on paper can fail if the course has few refill points, and a sodium number can be misleading if sweat rate was guessed from a cool training day.

Carbohydrate rate: Grams per hour planned during exercise. Moderate long sessions often start around 30 to 60 g/h, while longer or harder events may use 60 to 90 g/h when the athlete has practiced that intake.
Fluid rate: Liters per hour expected from bottles, cups, or a hydration pack. Sweat rate, heat, humidity, clothing, intensity, and personal tolerance all change the useful target.
Sodium replacement: Milligrams per hour supplied by drink mix, fuel, and capsules. It is a planning target, not an instruction to replace every milligram lost in sweat.

Carbohydrate, fluid, sodium, and repeat reminders arranged along an endurance route — Endurance fueling works best when hourly targets become small, repeatable actions rather than one large total saved for later.

The most common mistake is treating the highest published carbohydrate or sodium number as the right number. Higher carbohydrate intake often needs gut training and mixed carbohydrate sources. Higher fluid intake is useful only when it matches real sweat losses and stomach tolerance. Sodium matters most when sessions are long, hot, humid, or salty-sweat heavy, but adding salt does not make overdrinking safe. The practical goal is a plan that can be rehearsed in similar conditions, adjusted when the route or weather changes, and simple enough to follow while running or riding.

How to Use This Tool:

Choose Running or Cycling, enter the planned moving duration, and select the effort zone that describes most of the session rather than brief surges.
Set the carbohydrate target in grams per hour, then enter the prepared drink mix strength, bottle size, and carbohydrate in one gel, chew serving, bar segment, or other fuel unit.
Add sodium values for the drink and fuel unit. If you know your sweat sodium concentration, enter it directly; otherwise choose the low, medium, high, or very high profile that best fits your usual sweat pattern.
Open Advanced when the weather or athlete details matter. Body weight, temperature, humidity, measured sweat rate, salt capsule dose, and timeline interval all change the fluid, sodium, or reminder schedule.
Use the summary first, then check the Fueling Summary, Fueling Timeline, Carb Targets, Hydration Plan, and Fueling Strategy Map tabs before exporting CSV, DOCX, chart images, or JSON.

Interpreting Results:

Start with the per-hour badges because they are the easiest numbers to practice. Carbs in g/h, fluid in L/h, sodium in mg/h, bottles per hour, gels per hour, and salt capsules per hour show whether the plan feels physically executable. A plan that asks for more fluid than your gut can handle, more bottles than you can refill, or more gels than you can carry needs adjustment even if the total numbers look clean.

The Fueling Summary separates total needs from delivery sources. Total carbs show the full session demand, while drink carbs and solids carbs show how much comes from bottle mix versus gels or food. Bottles per hour and total bottles translate the fluid rate into carrying and refill logistics. Sodium shortfall is the remaining hourly sodium target after drink mix and fuel-unit sodium are counted, so a nonzero shortfall points to a capsule plan, a saltier drink mix, or a lower replacement target.

Treat warning badges as prompts to review the plan, not as automatic failures. A high fluid target means the rate is at least 1.5 L/h, which may be realistic for some hot, hard efforts but can be difficult to absorb. A high carb target appears above 110 g/h, a range that usually requires careful practice. A high sodium target appears above 1200 mg/h and should be checked against measured sweat rate, sweat sodium, weather, and medical context.

The timeline is the execution layer. Each row converts the same per-hour targets into the selected reminder interval, so a 20 minute row is one third of an hourly target and a 30 minute row is one half. Use those rows to decide when to sip, when to take a fuel unit, and when the plan needs simpler rounding. Rounding for real packets and bottles is expected; the useful plan is the one you can repeat consistently.

Technical Details:

Endurance fueling combines three linked rate problems. Carbohydrate intake supports working muscle and blood glucose, fluid intake offsets sweat loss, and sodium intake replaces part of the electrolyte loss that rises with sweat volume and sweat sodium concentration. The quantities interact because drink mix can provide both carbohydrate and sodium, while the chosen fluid rate determines how much of that mix is consumed each hour.

The planner uses minutes as the session input, converts duration to hours, and performs the main calculations as hourly rates. Measured sweat rate takes priority when entered. Without a measured value, the fluid estimate changes with temperature, humidity, sport, effort zone, and body weight, then stays inside a bounded planning range. Sweat sodium works similarly: a direct mg/L value takes priority, while the profile choices stand in for broad low to very high concentrations.

Formula Core:

The core arithmetic keeps the rate, total, and reminder-window views consistent. In the equations below, H is duration in hours, D is duration in minutes, F is fluid liters per hour, C is carbohydrate grams per hour, K is drink carbohydrate concentration in g/L, G is carbohydrate grams in one fuel unit, and Na is sodium.

Quantity	Formula	Meaning
Duration in hours	$H = \frac{D}{60}$	Converts planned minutes into the multiplier used for totals.
Total carbohydrate	$C_{total} = C_{h} H$	Multiplies the hourly carbohydrate target by total hours.
Drink carbohydrate per hour	$C_{drink, h} = F K$	Fluid L/h multiplied by prepared drink mix grams per liter.
Fuel-unit carbohydrate per hour	$C_{solid, h} = \max (0, C_{h} - C_{drink, h})$	Assigns only the carbohydrate not covered by drink mix to gels, chews, bars, or food units.
Fuel units per hour	$U_{h} = \frac{C_{solid, h}}{G}$	Divides the remaining carbohydrate rate by grams in one fuel unit. A zero-size fuel unit returns zero units.
Sodium target per hour	${Na}_{target, h} = 0.70 F {Na}_{sweat}$	Uses 70 percent of estimated sweat sodium loss as the replacement target.
Sodium shortfall per hour	${Na}_{gap} = \max (0, {Na}_{target, h} - (F {Na}_{drink} + U_{h} {Na}_{unit}))$	Subtracts sodium supplied by drink and fuel units before calculating any capsule need.
Reminder-window amount	$X_{window} = X_{h} \frac{T_{window}}{60}$	Converts hourly carbs, drink volume, sodium, and fuel units into each reminder interval.

Fluid and Sodium Rules:

Rule	Applied behavior	Why it matters
Measured sweat rate	A positive measured L/h value replaces the environmental estimate.	Field testing under similar conditions is usually more useful than a generic estimate.
Estimated fluid range	The environmental estimate is bounded from 0.25 to 2.5 L/h.	The bound prevents extreme weather or input combinations from producing implausible planning rates.
Sodium profile	Low, medium, high, and very high profiles map to 300, 600, 900, and 1200 mg/L unless a direct sweat sodium value is entered.	Profiles provide a rough stand-in when no lab or field estimate is available.
Warning thresholds	Fluid at 1.5 L/h or higher, carbohydrate above 110 g/h, and sodium target above 1200 mg/h trigger a caution badge.	Those values may be appropriate for some athletes, but they deserve a tolerance and logistics check.
Strategy bands	Carbohydrate below 60 g/h is conservative, 60 to 90 g/h is endurance, and above 90 g/h is aggressive.	The Fueling Strategy Map shows where the current plan sits relative to broad carbohydrate guidance.

Worked Mechanism Path:

For a 180 minute ride at 80 g/h, duration is 3 hours and total carbohydrate is 240 g. If fluid is 0.75 L/h and the prepared drink contains 60 g/L, drink mix supplies 45 g/h. The remaining 35 g/h comes from fuel units. With 25 g in one gel or serving, that is 1.4 units per hour and 4.2 units across the ride before practical rounding.

If the same ride uses a 500 mL bottle, 0.75 L/h becomes 1.5 bottles per hour and 4.5 bottles total. With sweat sodium at 900 mg/L, the sodium target is 0.70 x 0.75 x 900, or about 473 mg/h. A drink containing 500 mg/L supplies 375 mg/h, and 1.4 fuel units with 100 mg sodium each add 140 mg/h, so there is no remaining capsule shortfall in that example.

Limitations, Privacy, and Accuracy Notes:

Endurance fueling is individual. Gut tolerance, heat acclimation, altitude, medical history, medication use, menstrual cycle effects, course access, aid-station products, and event rules can all change the final plan. The output is a planning baseline for healthy adults, not a medical prescription, and it should be practiced during training before race day.

Sweat-rate estimates are broad. A better field method is to weigh before and after a similar session, account for fluid consumed and urine produced, and repeat the test in different weather and intensity conditions. Sodium profiles are even rougher because sweat sodium varies widely between athletes. Use a measured value when sodium planning is important, especially for long, hot, or remote events.

The entered values are processed in the browser, and exports are generated from the current page state. Avoid sharing exported files more widely than intended, especially when they include personal sweat-rate or fueling details. Keep the exported plan practical by rounding to real bottle fills, packet sizes, and aid-station timing.

Worked Examples:

A 2 hour run at 60 g/h needs 120 g of carbohydrate total. If the runner drinks 0.6 L/h of a 40 g/L mix, the bottle supplies 24 g/h. The remaining 36 g/h can be handled as roughly one and a half 25 g gels per hour, or rounded into a repeatable pattern such as one gel every 25 to 30 minutes plus drink sips.

A 5 hour gravel ride at 90 g/h needs 450 g of carbohydrate total. If the rider can refill often, a 70 g/L mix at 0.8 L/h supplies 56 g/h, leaving 34 g/h from bars, chews, or gels. The timeline helps turn that into smaller windows so the rider is not trying to remember a five hour total while climbing, descending, or moving through aid stops.

A hot 3 hour run with a measured sweat rate of 1.2 L/h and a very high sweat sodium profile produces a large sodium target. If drink mix and gels do not cover much of it, the sodium shortfall and salt-cap rate show the scale of the remaining plan. That is a cue to test the strategy in similar heat, not to add capsules blindly on race day.

FAQ:

Should every long session use 90 g/h of carbohydrate?

No. Higher carbohydrate targets can help in long or intense events, but they need gut training and product testing. Many athletes start lower, then increase gradually as tolerance improves.

Why does measured sweat rate change the plan so much?

Fluid and sodium targets scale from sweat loss. A measured sweat rate from similar weather and intensity usually gives a better starting point than a broad estimate.

Does the sodium target mean full sodium replacement?

No. The sodium target is based on partial replacement of estimated sweat sodium loss. Replacing every milligram is not usually practical or necessary, and overdrinking can still be dangerous even when sodium is included.

Can I use a bar or chews instead of gels?

Yes. Enter the carbohydrate and sodium in one planned serving and treat that serving as the fuel unit. The math is the same whether the unit is a gel, chew serving, bar segment, or other portable food.

Why do total bottles or gels show decimals?

Decimals preserve the calculation before real-world rounding. Use them to decide whether to carry an extra bottle, split a serving, refill earlier, or simplify the timeline.

Glossary:

Carbohydrate target: Planned carbohydrate intake in grams per hour during the run or ride.
Drink concentration: Grams of carbohydrate or milligrams of sodium in each liter of prepared drink after mixing.
Fuel unit: One gel, chew serving, bar segment, or other repeatable food portion used to fill the carbohydrate gap after drink mix.
Sweat rate: Estimated or measured fluid loss per hour, expressed in liters per hour.
Sweat sodium: Sodium concentration in sweat, expressed as milligrams per liter.
Sodium shortfall: Remaining hourly sodium target after sodium from drink mix and fuel units has been counted.

References:

Nutrition and Athletic Performance, Dietitians of Canada, Academy of Nutrition and Dietetics, and American College of Sports Medicine.
International Society of Sports Nutrition position stand: nutrient timing, Journal of the International Society of Sports Nutrition.
National Athletic Trainers' Association Position Statement: Fluid Replacement for the Physically Active, Journal of Athletic Training.
Wilderness Medical Society Clinical Practice Guidelines for Exercise-Associated Hyponatremia, Wilderness and Environmental Medicine.