Cycling fueling calculator
Enter your ride. Get bottles, gels, sodium and what to wear.
Your ride
Why these carb targets?
Your gut can only absorb so much carbohydrate an hour. One carb type (glucose or maltodextrin) tops out near 60 g/hr; glucose + fructose blends reach about 90 g/hr.
ResearchJeukendrup, 2008Jeukendrup, 2014 Our ruleYour setup
Adjust for todayoptional
Temperature, heat, bottles, first gelTemperature when there's no forecast
Why the cap stops at 8%
Repeated 8% drinks slowed gastric emptying; weaker ones didn't. The app never goes above 8%, even with an override.
ResearchMurray et al., IJSNEM 1999I know what I like
My setup: your carb bottles and the grams of carbs in each. The plan solves the gels around them to hit your carb target. Changing a number pins it.
About you
For your race age group and percentile labels. Both optional; stored on this device only.
Fueling targets
Why these numbers?
Your gut can only absorb so much carbohydrate an hour. One carb type (glucose or maltodextrin) tops out near 60 g/hr; glucose + fructose blends reach about 90 g/hr.
ResearchJeukendrup, 2008Jeukendrup, 2014 Our ruleWhat's typical?
How salty you sweat is a personal trait: roughly 200–2,000 mg per liter, about 1,000 typical. A sweat test measures yours. Loss per hour is that times how much you sweat, so the target follows your fluid.
ResearchBaker, 2017How to measure it
Weigh yourself right before and after a ride, in minimal kit and towelled dry. Each pound lost is about 15 oz of sweat (1 kg ≈ 1 L). Add what you drank, then divide by the hours. The Journal's weigh-in does the math.
GuidelineACSM, 2007 Our ruleHow the timing works
Caffeine peaks 30–60 min after a dose and takes about 5 hours to halve, so a mid-ride dose still covers the finish. 3–6 mg per kg of body weight helps endurance; above ~9 mg/kg adds side effects, not speed.
GuidelineISSN, Guest et al., 2021 ResearchCox et al., 2002What you carry
Fine-tune
Why alternate?
Alternating is for a change of form. A chew or a bite of food between gels breaks up hours of the same sweet texture; a second gel only changes the wrapper, so items of the same form are not listed.
Our ruleSwitching form does not cost you fuel: in a lab study at 120 g/h, carbs from chews, gels and a drink were used at the same peak rate.
Bikes
how many bottles you can leave withHow bottle roles work
Each cage gets a role. Carb bottles get the drink mix. An Electrolyte bottle gets the sodium top-up and no carbs, and gels land on the half hour with a sip of it, so gel and carb drink don't stack. Water bottles carry nothing.
Fluid splits by cage count (Electrolyte, Carb, Carb = 1/3 and 2/3), refills included. With every cage on Carb, the plan works exactly as before.
Our ruleMedications
Some medications change how you handle heat, fluid and sodium. Tick what applies and the plan flags what to watch; it never changes a number.
GuidelineCDC: Heat & medicationsStays on this device and in your journal entries, never on the shared image. A flag, not medical advice.
Product library
Everything the dropdowns above pull from. Tap ☆ on what you ride with and it floats to the top. Edit an item when a label changes.
Gels & solid fuel
Per serving, including gels that carry sodium.
Drink mixes
Per serving of powder. Grams of powder ≠ grams of carbs.
My bottles
Aero bottles, packs, soft flasks: any size besides 28 oz and 1 L. They join the bottle dropdowns.
Sodium top-ups
Closes the sodium gap. Capsules are swallowed on a schedule; salt and tablets go in the bottles.
Closet
what goes on, at what feels-likeAdvancedunits · caps · rounding · races backup
Units
Temperature → bottle concentration cap
Do-not-exceed caps: grams of carbs per 100 mL.
- 3%Hot
Fluid first. A little carb (1–3%) speeds fluid absorption.
ResearchBaker, GSSI 2023 - 6%Moderate
Above 6%, fluid delivery drops, and adding sodium doesn't fix it.
ResearchJeukendrup et al., 2009 - 8%Ceiling
Repeated 8% drinks slowed gastric emptying. The app never goes above 8%.
ResearchMurray et al., IJSNEM 1999
Band thresholds: weather lookup (WBGT)
Wet bulb globe temperature is the heat-stress index ACSM, OSHA, the military and NWS use. Unlike the heat index, it counts sun and wind.
GuidelineNWS: WBGTBand thresholds: typed feels-like
Anything in between is Moderate.
Our ruleGel rounding
Races backup
Your races as a JSON file, to keep or move to another device. Importing merges by race: the newer edit wins, and a different race with the same date and name asks first.
Journal
One row per ride, newest first. Tap a row to see the full log.
Races
Your results, PRs and age group, from your own race history.
Your races
The science
What we stand on
Every number in the calculator stands on one of these beliefs. Tap one to see the evidence.
Bottles never go above 8% carbsResearch
What we believe
A little carbohydrate helps fluid absorb, but stronger drinks slow fluid delivery. So the hotter the day, the weaker the bottle, and 8% is the ceiling.
Why
A small amount of carbohydrate (1–3%) speeds fluid absorption, while drinks at 8% and above delay fluid delivery. Glucose + fructose blends soften that at higher concentrations.
GSSI SSE #244, Baker (2023)Fluid delivery was compromised once concentration went above 6%, and adding sodium didn't fix it.
Jeukendrup et al., 2009Repeated drinking of an 8% carb beverage during exercise significantly slowed gastric emptying; lower concentrations didn't.
Murray et al., IJSNEM 1999
What the app does
Hot: 3% (fluid first). Moderate: 6%. Cold: 8%, and the app will not go higher. Our old 10% cold band was a tolerance habit, not evidence.
Heat cuts how much carb you can useResearch
What we believe
In the heat your body burns less of the carbohydrate you take in, and your stomach empties more slowly.
Why
Cyclists at 35°C vs 16°C oxidized less of the carbohydrate they drank and burned 25% more muscle glycogen.
Jentjens et al., J Appl Physiol 2002Runners in the heat used ~20% less ingested carbohydrate even with hydration kept normal.
Mougin et al., 2025In a 49°C (120°F) room, water left the stomach more slowly than at 18°C, tracking rising core temperature. At 35°C it slowed only when riders were dehydrated.
Neufer et al., Eur J Appl Physiol 1989
What the app does
The "Heat: lower carb target ~15%" toggle. Off by default; the app nudges you in the Hot band.
Above 60 g/hr you need glucose + fructoseResearch
What we believe
One kind of sugar tops out around 60 g/hr because the gut can only absorb it so fast. Going higher takes a glucose + fructose mix.
Why
A single carbohydrate type tops out around 60 g/hr because its intestinal transporter saturates; glucose + fructose together can push oxidation to ~105 g/hr.
Jeukendrup, Eur J Sport Sci 2008~60 g/hr for 2–3 hr efforts; ~90 g/hr for ultra-endurance, only with multiple transportable carbohydrates.
Jeukendrup, Sports Med 2014GSSI SSE #106
What the app does
Red warning if a single-source product is used above 60 g/hr. Note above 90 g/hr. The library tags each product's carb type.
Two sugars beat one, and your gut is trainableResearch
What we believe
Glucose and fructose enter through different doors in the gut, so a blend gets more fuel in than either one alone. How much your gut handles can be trained: build up to a high carb target in training, not on race day.
Why
Glucose (and maltodextrin, which is chains of glucose) is absorbed by one transporter that saturates around 60 g/hr. Fructose uses a different one, which is why blends go higher.
Jeukendrup, Eur J Sport Sci 2008Jeukendrup, Sports Med 2014Cyclists drinking carbohydrate at a very high rate burned a glucose + fructose drink at a peak of about 1.75 g/min (roughly 105 g/hr), about 65% more than glucose alone (1.06 g/min).
Jentjens & Jeukendrup, Br J Nutr 2005A 2:1 glucose:fructose drink improved time-trial performance by 8% over the same amount of glucose alone.
Currell & Jeukendrup, MSSE 2008Across 14 studies, fructose + glucose drinks (0.5–1 part fructose per part glucose) gave small to moderate gains in power (1–9%) over glucose alone, and better gut comfort.
Rowlands et al., Sports Med 2015The gut adapts. Gastric emptying and stomach comfort can be trained, and how much carbohydrate the gut absorbs follows what you regularly eat.
Jeukendrup, Sports Med 2017In races, athletes who took in more carbohydrate reported more nausea and flatulence; in Ironman races they also finished faster.
Pfeiffer et al., MSSE 2012Form is about comfort, not fuel: at 120 g/hr, carbohydrate from a drink, gels and chews was burned at the same peak rate.
Hearris et al., J Appl Physiol 2022The 10 g/hr trigger, the 2–3 week build-up, the 2-hour line and the nudge toward a second form (in a plan note, and in alternating only between forms) are our rules of thumb, not study findings.
Our rule
What the app does
Each product can carry the glucose:fructose ratio its label states; it stays blank when the label doesn't say. On a ride of 2 hours or more, when every carb in the plan is one form at one ratio, a note suggests a second form or carb type (not on a No gels day, when you have chosen bottles only). Fine-tune alternates only between different forms. When today's plan is more than 10 g/hr above the most you have logged on a ride, a note suggests stepping up over 2–3 weeks. Both are notes only: the app never changes your numbers for them.
Age groups, percentiles and PRsOur rule
What we believe
A result means more when it's compared fairly: with your own age group, against the share of the field you beat, and only with legs that were raced as advertised.
Why
Age group: IRONMAN and USA Triathlon place you by your age on December 31 of the race year, so your group stays the same all season. Bands are 18–24, then five-year bands (25–29 … 75–79), then 80+.
Race rulesPercentile is the share of the field you beat: (1 − place ÷ finishers) × 100. 22nd of 180 beats 88% of the age group. Higher is better. Imported spreadsheet percentiles where lower was better are flipped the same way.
Our ruleFairness flags keep PRs honest: a current-assisted swim, a short or long leg, or an altered course (like a cancelled swim) is left out of that leg's PR and out of the overall PR for the distance. It can still earn a course best. A wetsuit is not a flag: wetsuit swims count.
Our ruleHeat-adjusted run: run time is scaled by the dew point, 0% below 60°F, 1% at 60–64, 2% at 65–69, 3.5% at 70–74 and 5% at 75 and up, then compared. The bands are adapted from the athlete's own method: a heuristic, not a published model.
Heuristic
What the app does
Each race shows its age-group band from your birthday; the Summary has Current age group and All time views. Percentiles and ranks are computed from place and finishers, never stored. Wins lines only use unflagged legs for PRs, need at least two earlier comparable races, and are never negative.
Drink to your sweat rate, not a weather formulaGuideline
What we believe
Every rider sweats differently, so your measured sweat rate beats any formula. The goal is to keep body-water loss under 2%.
Why
ACSM: drink to keep body-water loss under 2%, typically 400–800 mL/hr depending on sweat rate and size, with sodium around 0.5–0.7 g per liter. Sweat rates vary so much that a measured sweat test beats any formula.
ACSM Position Stand, 2007For events over ~4 hr, replace 50–80% of the sodium you lose in sweat.
McCubbin, via CTSWarmer air raises sweat rate about 0.04 L/hr per °C. Outdoor prediction also needs sun, wind, humidity, speed and body size, and is still only about ±0.45 L/hr, so weighing yourself on your own rides is sharper.
Exp Physiol 2023J Appl Physiol 2024
What the app does
Fluid checks at 0.4 / 0.8 / 1.2 L/hr. A sweat-rate field in Profile, not a weather formula. "Feels-like" temperature is the one weather input because your weather app already folds in humidity and wind.
Sodium follows sweatResearch
What we believe
Sweat saltiness is personal. Your hourly sodium loss is that saltiness times how much you sweat, so it rises when you sweat more.
Why
Sweat sodium concentration is an individual trait (roughly 200–2,000 mg/L; ~1,000 is typical) and is what a sweat test reports. Hourly loss is that concentration times sweat volume, so it rises with heat, and concentration itself creeps up at higher sweat rates as ducts reabsorb less.
Baker, 2017
What the app does
Profile stores mg/L; the plan multiplies by today's fluid, so a Hot-day fluid bump raises the sodium target with it. Drinking more plain water at a fixed sodium intake is the recipe for dilutional hyponatremia.
Heat stress is WBGT, not feels-likeGuideline
What we believe
Heat stress depends on sun, wind and humidity as well as air temperature. WBGT counts all of them; the heat index assumes shade.
Why
Wet bulb globe temperature is the heat-stress index used by ACSM, OSHA, the U.S. military and NWS. It combines temperature, humidity, wind and solar radiation; the heat index assumes shade.
NWS Tulsa: WBGTNWS: WBGT vs heat indexOur estimate uses the same method as NWS's national WBGT forecast: the Dimiceli–Piltz black-globe equation with the Hunter–Minyard natural wet bulb, fed by Open-Meteo's hourly temperature, humidity, wind and solar radiation.
NDFD WBGT algorithm (Boyer, NWS/MDL)For U.S. locations the app first asks NWS for its own operational WBGT forecast (an NDFD element since June 2022) and uses that; elsewhere, or if NWS doesn't answer, it estimates with the same method. The finding says which one you got.
NWS Service Change Notice 22-43
What the app does
When you use the weather lookup, the concentration band is set by average WBGT over your ride window (defaults: Hot ≥ 80°F, Cold < 60°F WBGT). Typed temperatures still use the feels-like thresholds. It's a forecast-based estimate, not a globe thermometer; shade, pavement and local wind move the real number.
Caffeine goes where it works: the back halfResearch
What we believe
Caffeine should be peaking when fatigue sets in. On a long ride, that's the back half.
Why
The ISSN position stand: 3–6 mg/kg taken about 60 minutes before it is needed improves endurance performance; doses above ~9 mg/kg add side effects, not benefit.
Guest et al., 2021Plasma caffeine peaks 30–60 minutes after a dose and has a half-life of roughly 5 hours, so a dose in the first hour still works in hour four but is fading. Late-exercise doses restore performance when fatigue sets in.
Cox et al., 2002
What the app does
Short rides get the caffeinated gel first. Rides over 2.5 h get the first dose so its window covers the back half (about 90 minutes in on a 4-hour ride), then one more every ~2.5 h if the rider's per-ride cap allows. Nothing after the rider's cutoff time. The app never adds caffeine unless it is switched on in Profile, and never adjusts carbs or sodium for it.
Small and often beats big gulpsResearch
What we believe
Small, regular drinks keep fluid and fuel moving through your stomach. Big gulps of strong drink slow it down.
Why
Serial small drinks empty steadily; big boluses of strong solution do not.
NASEM review
What the app does
Minimum gels per hour and even spacing. The exact "1 per hour" and "first gel at 20 min" are practice, not a paper.
Medications get a flag, never a number changeGuideline
What we believe
Some common medications make heat harder to handle, but there's no evidence for a specific fueling change for any one drug.
Why
Clinician guidance groups heat-sensitizing drugs by mechanism: SSRIs/SNRIs (impaired central thermoregulation, more sweating, dehydration and electrolyte risk), tricyclics and antipsychotics (reduced sweating), ADHD stimulants (more heat production), beta blockers (impaired skin blood flow), ACE inhibitors and GLP-1 agonists (blunted thirst), diuretics and lithium (fluid and electrolyte loss), first-generation antihistamines (reduced sweating).
Americares / Harvard C-CHANGE provider guideNYC Health: Heat and MedicationsDrug Topics summaryThe drug-name lookup uses the consolidated list from the Arizona Heat Preparedness Network's Heat and Medications sheet for providers (ADHS, Pima County, UArizona), which draws on CDC's clinician guidance.
CDC: Heat and Medications — Guidance for CliniciansWe found no study that gives a specific fueling adjustment for any drug, so the app flags the mechanism and never changes a number.
Our rule
What the app does
The app flags the mechanism and what to watch; it never changes a number because of a medication. Talk to your prescriber about training in heat.
Where the evidence runs out, we say soOur rule
What we believe
Some numbers in the app are our judgment call, not a finding. We'd rather tell you than dress them up.
Why
The exact temperature breakpoints (85°F, 65°F) are ours. Whether 8% is fine for you on a cold day is your gut. Per-person sodium needs vary several-fold.
Bottle roles are our call too: splitting fluid by cage count, and the warning when an electrolyte bottle passes ~1,500 mg sodium per liter. We found no study that sets how salty a bottle drunk with gels can be; the concern that a very salty drink plus a gel makes the gut contents hypertonic is reasoning, not a measured limit.
What the app does
Anything tagged Our rule is practice, not a paper. Use the journal to find what works for you.
Coach's guidance: 75–85 g/hrOur rule
What we believe
Aim for 75 g/hr on easy rides and 85 g/hr on long rides with intervals.
Why
From Bluebird Multisport: don't plan below 75 — the difference in recovery and how you feel is real.
What the app does
The intensity presets start at 75, 85 and 90 g/hr; you can change them in Profile.
Disclaimer
Bluebird Fuel is a planning tool, not medical advice. The numbers come from published sports-nutrition research (see the beliefs above) and from product labels you or we entered; your tolerance for carbs, fluid and sodium is individual and is yours to test in training before racing. Brands reformulate — check the label. If you have a medical condition affecting hydration, electrolytes or blood sugar, talk to a clinician.
About
Bluebird Fuel is free. Nothing leaves your device: your products and journal are saved in this browser only. Use Back up on the Journal tab to keep a copy. On iPhone, add this page to your Home Screen so it behaves like an app and keeps its data.