Endurance Fuel Planner

Fueling Snapshot

{{ sportLabel }} · Zone {{ intensity_zone }}

Carbs {{ carb_target_gph }} g/h Drink {{ Math.round(drink_carb_gph) }} g/h Solids {{ Math.round(solids_carb_gph) }} g/h Fluid {{ fluid_lph_display }} L/h {{ bottles_per_h_display }} × bottle/h {{ gels_per_h_display }} × gel/h Drink {{ Math.round(drink_carb_g_per_l) }} g/L · {{ Math.round(drink_sodium_mg_per_l) }} mg/L {{ salt_caps_per_h_display }} × salt cap/h

Sport:

Duration: min

Body weight: kg

Intensity zone:

Carb target: g/h

Drink mix: g/L

Bottle size: mL

Gel carb: g

Drink sodium: mg/L

Gel sodium: mg

Temperature:

°C

Humidity:

Measured sweat rate:

L/h

Sweat sodium:

mg/L

Salt cap dose:

Timeline interval:

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 timeline yet.

Tags: Cycling , Running

Export to PDF Fullscreen

Embed:

Endurance fueling needs are the carbohydrate, fluid, and sodium you plan to take in during long efforts so your pace holds steady and your head stays clear. Many athletes think of this as a marathon and long ride nutrition plan that turns conditions and goals into simple hourly targets.

Planning starts with what the effort demands and then assigns drink, gels, and salt so intake matches sweat and energy use. You provide a session length, your weight, an effort zone, and the strength of your bottle mix, then you refine with gel size, bottle volume, and sodium.

Results show per hour targets and totals for carbs, fluid, and sodium plus a block by block timeline that you can copy out for a race plan. If numbers look unusual, change only one input at a time and compare like for like conditions so the differences make sense.

A short example helps the idea land. A two hour tempo run in warm weather may call for roughly half your carb target from drink, the rest from gels, and about one and two thirds bottles per hour when mix strength is moderate.

Caution. Valid patterns do not guarantee comfort or safety, so test on easy days and adjust slowly. This tool provides informational estimates and does not substitute professional advice.

Technical Details:

Fueling for steady endurance work combines three quantities observed over time: carbohydrate intake, sweat volume, and sweat sodium concentration. The planner focuses on per hour rates so totals scale cleanly with duration and conditions remain comparable within a session.

When no measured sweat rate is provided, fluid loss is estimated from temperature, humidity, effort zone, sport, and body mass. From fluid rate and drink mix strength it computes how many grams of carbohydrate come from bottles, how many remain for solids, how many gels that implies, and how many bottles per hour cover the fluid target.

Electrolyte guidance targets partial sodium replacement rather than a full match. The sodium goal per hour is set as seventy percent of the estimated sweat sodium loss, with any shortfall expressed as the number of salt capsules needed based on your capsule size.

Flags appear when targets cross simple guardrails that mark aggressive plans. High fluid appears at 1.5 L/h and above, high carbohydrate above 110 g/h, and high sodium target above 1200 mg/h. Values near these edges deserve extra testing and attention.

\begin{array}{l} F = clamp (B + A) \times H \times Z \times S \times W, 0.25, 2.5 \\ B = 0.35 \\ A = {t \geq 10 \to (t - 10) \times 0.03, t < 10 \to (t - 10) \times 0.015} \\ H = 1 + ((h - 40) / 100) \times 0.6 \\ Z = {Z1 \to 0.85, Z2 \to 1.00, Z3 \to 1.20, Z4 \to 1.40, Z5 \to 1.60} \\ S = running \to 1.00, cycling \to 0.90 \\ W = clamp ((w / 70)^{0.25}, 0.85, 1.25) \end{array}

Symbols and units
Symbol	Meaning	Unit/Datatype	Source
t	Ambient temperature	°C	Input
h	Relative humidity	%	Input
w	Body mass	kg	Input
Z	Effort zone multiplier	ratio	Derived from zone
S	Sport multiplier	ratio	Derived from sport
W	Weight multiplier	ratio	Derived
F	Fluid target rate	L/h	Estimated or measured
C_target	Carb target rate	g/h	Input
C_drink	Drink carbohydrate rate	g/h	Derived
C_mix	Drink mix strength	g/L	Input
G_gel	Carbs per gel	g	Input
V_bottle	Bottle volume	mL	Input
S_sweat	Sweat sodium concentration	mg/L	Input or profile
S_target	Sodium target rate	mg/h	Derived
T	Session duration	h	Input

Worked example. Running, 2 h, 70 kg, Zone 3, 20 °C, 50 %. Estimated fluid F ≈ 0.83 L/h. With C_mix=60 g/L, drink provides ≈ 50 g/h and solids ≈ 40 g/h. With G_gel=25 g, gels ≈ 1.62 /h. With V_bottle=500 mL, bottles ≈ 1.65 /h and total ≈ 3.31 over 2 h. With S_sweat=600 mg/L, S_target ≈ 347 mg/h; drink sodium ≈ 413 mg/h and gel sodium ≈ 162 mg/h yield no shortfall.

\begin{array}{l} S {target}_{} = 0.7 \times F \times S_{sweat} \\ C_{drink} = F \times C_{mix} \\ C_{solids} = \max (C_{target} - C_{drink}, 0) \\ Gels per hour = C_{solids} / G_{gel} \\ Bottles per hour = F \times 1000 / V_{bottle} \end{array}

Interpretation thresholds
Threshold band	Lower	Upper	Interpretation	Action cue
Fluid high	1.50 L/h	No cap	Aggressive fluid replacement	Test stomach comfort and bottle access
Carb high	110 g/h	No cap	Very high carbohydrate target	Build gradually during training
Sodium target high	1200 mg/h	No cap	Large replacement goal	Consider drink mix and capsules together

Units, precision, and rounding:

Numbers display with locale grouping and up to two decimals for most fields.
Timeline rounds per block to 1 g carbs, 10 mL drink, and 10 mg sodium.
Gels per block round to 0.5; whole session totals multiply per hour rates by duration.

Validation and bounds:

Inputs and validation
Field	Type	Min	Max	Step/Pattern	Placeholder
Sport	Select: running or cycling	—	—	Fixed options	—
Duration	Number	1 min	—	Step 1	120
Body weight	Number	30 kg	—	Step 0.5	70
Intensity zone	Select Z1 to Z5	1	5	Fixed options	—
Carb target	Number	0 g/h	—	Step 1	90
Drink mix strength	Number	0 g/L	—	Step 1	60
Bottle size	Number	100 mL	—	Step 10	500
Gel carbohydrate	Number	0 g	—	Step 1	25
Drink sodium	Number	0 mg/L	—	Step 10	500
Gel sodium	Number	0 mg	—	Step 10	100
Temperature	Number	—	—	Step 0.5	—
Humidity	Number	0 %	100 %	Step 1	—
Measured sweat rate	Number	0 L/h	—	Step 0.05	—
Sweat sodium	Number	0 mg/L	—	Step 10	—
Sodium profile	Select	—	—	Low, Medium, High, Very High	—
Salt capsule size	Number	0 mg	—	Step 10	200
Timeline interval	Number	5 min	—	Step 5	30

I/O and encoding:

Inputs accept numbers in the units shown and fixed options for sport, zone, and sodium profile.
Outputs present on screen rates and totals, a timeline, and optional CSV or JSON for export.

Networking and storage:

All calculations run in your device; no requests are sent to a server.
Copy and download actions use the clipboard and file downloads provided by your device.

Assumptions and limitations:

Heuristic fluid model; measured sweat rate overrides the estimate.
Estimate clamps only the computed fluid rate, not a measured input.
Sodium target uses 70% of loss; profiles map to ~300, ~600, ~900, ~1200 mg/L.
Mixing assumes even concentration in bottles and steady sipping.
Totals scale linearly with duration; conditions are treated as constant.
No adjustment for wind, sun, altitude, or clothing.
Zone mapping is coarse; individual response varies.
Weight effect is modest via a fourth‑root multiplier.
Heads‑up Gels per hour may be fractional; timeline provides block guidance.
Heads‑up Negative sodium shortfall is treated as zero.

Edge cases and error sources:

Duration set to zero hides results.
Humidity outside 0 to 100 is clamped.
Zones outside 1 to 5 are clamped.
Very cold inputs reduce the warm component but not below the base clamp.
Measured sweat rate can exceed the estimate limits; review feasibility.
Gel carbohydrate set to zero yields zero gels.
Very weak mixes push most carbs to solids.
Bottle size too small inflates bottle count unrealistically.
Timeline rounding may make per block sums differ slightly from totals.
Ties round to the nearest step using standard half‑up behavior.
Last timeline block shortens when duration is not a multiple of the interval.
Locale number formatting may change grouping and decimal separators.

Privacy & compliance:

No data is transmitted or stored server‑side.

How‑to · Plan a session:

Set the concept first: match intake to sweat and energy with simple rates and totals.

Choose running or cycling and enter duration.
Enter body weight and pick an effort zone.
Set a carbohydrate target per hour.
Enter drink mix strength and bottle size.
Enter gel size and sodium values for drink and gel.
Optionally add temperature, humidity, measured sweat, and sodium profile.
Pick a timeline interval and review metrics, timeline, and charts.

Example: 120 min, 90 g/h, 60 g/L, 500 mL bottle, 25 g gel, drink sodium 500 mg/L, gel sodium 100 mg.

Use the per hour rates to stock bottles and gels, then follow the timeline in training.

FAQ:

Is my data stored?

No. Calculations run locally and copy or download actions happen on your device. Nothing is sent to a server.

How accurate is the estimate?

The fluid model is heuristic and responds to weather, effort, sport, and weight. A measured sweat rate gives the best fit for you.

What units are used?

Carbs in g/h, fluid in L/h, sodium in mg/h or mg/L, duration in minutes, timeline in minutes.

Can I plan without gels?

Yes. Set gel carbohydrate to zero and the plan assigns all solids to other foods while keeping drink math unchanged.

Why do I see a warning?

Crossing the high bands means the plan is demanding. Build up slowly and test comfort before using those targets in events.

How do I calculate sodium per bottle?

Multiply drink sodium concentration by bottle volume and divide by 1000. Compare that to the sodium target rate and your timeline blocks.

Does this work offline?

Once loaded, calculations work without a connection. Copy and download features also work without a connection.

What does “borderline” mean?

Results near a threshold can swing with small changes in inputs. Treat them as starting points and confirm during easy sessions.

Troubleshooting:

No results shown: ensure duration is at least 1 minute.
Unrealistic bottles per hour: check bottle size and mix strength.
Zero gels but solids expected: set gel carbohydrate above zero.
High sodium target: review sodium profile and drink sodium.
Very high fluid target: lower intensity, temperature, or humidity to match conditions.
Totals do not match mental math: remember timeline rounding per block.

If inputs contain text or symbols instead of numbers, replace them with valid numeric values in the shown units.

Advanced Tips:

Tip Use a measured sweat rate for key events and save the estimate for training days.
Tip Align the timeline interval with your course aid spacing to cut mental math.
Tip Move carbs from drink to solids by lowering mix strength if fluid needs are modest.
Tip Nudge sodium with capsules only after optimizing drink sodium and gel sodium.
Tip Keep weather inputs consistent when comparing sessions across weeks.
Tip For long rides, test a larger bottle size to reduce handoffs and stops.

Glossary:

Carbohydrate target: Grams per hour you plan to consume.
Drink mix strength: Grams of carbohydrate per liter of fluid.
Sweat rate: Liters of sweat lost per hour.
Sweat sodium: Sodium concentration of sweat in mg/L.
Salt capsule: A set dose of sodium used to cover shortfall.
Effort zone: A five‑step scale for perceived intensity.
Bottles per hour: How many full bottles meet fluid needs.
Gels per hour: How many gels cover remaining carbs.