What the calculator does, and what it does not do

Inputs and outputs

You choose any water volume from 250 to 1,500 mL (with quick picks for common bottle sizes), 10–150 g of carbohydrate, an expected bottle duration from 15 minutes to 4 hours, a pathway ratio and the ingredients available. The calculator returns the weight of each ingredient, total powder, glucose- and fructose-pathway equivalents, grams per hour, grams per 100 mL, sodium per bottle, sodium per litre, sodium per hour and estimated osmolality. The optimiser's internal particle score is not displayed; the osmolality figure is the same model expressed in mOsm/kg.

Changing a custom bottle's water volume leaves the carbohydrate grams unchanged. Suggested electrolyte and texture amounts rescale with the water; an amount you typed stays as typed until you ask for the suggestion back. Commercial-inspired presets scale their displayed amounts with water to preserve the reference concentration. A batch control multiplies the weigh list for 5 or 10 bottles of dry premix, which is the practical way to weigh sub-gram amounts.

Carbohydrate pathway bookkeeping

The pathway labels are a simplified way to compare carbohydrate sources commonly discussed in endurance research. They are not direct measurements of intestinal absorption.

target fructose share = fructose ÷ (glucose + fructose)

The allocator searches only the selected ingredients. If they cannot make the chosen ratio, it shows the closest possible mixture and reports both the target and achieved ratios.

Particle score and estimated osmolality

The optional optimiser compares the ideal number of dissolved particles before digestion. Its relative factors are 1.0 for anhydrous dextrose and fructose, 0.526 for sucrose, 0.1 for representative DE10 maltodextrin, 2.45 for trisodium citrate dihydrate and 6.17 for table salt.

particle score = Σ(ingredient grams × relative factor) ÷ water litres

The score has no units and is used only inside Mix My Bottle to choose between blends. The displayed osmolality estimate converts the same ideal particle model using anhydrous glucose as the reference:

estimated mOsm/kg added water = particle score × (1000 ÷ 180.156)

This assumes 1 mL of water weighs 1 g, complete dissolution, full electrolyte dissociation and representative DE10 maltodextrin. Alginate and pectin are excluded because chain length, substitution and ionisation vary by grade. Dextrose monohydrate also weighs differently from the anhydrous dextrose used in the model.

Sodium target and sources

The builder works from a sodium concentration target in milligrams per litre of water, scaled to the bottle: Light 350 mg/L, Standard 500 mg/L (the default), Heavy 700 mg/L, or a custom value up to 1,500 mg/L. The Standard and Heavy tiers sit inside the ACSM 0.5–0.7 g/L range for exercise beyond an hour. Standard also sits inside the Australian Institute of Sport 230–690 mg/L standard sports drink band; Heavy is just above it. Sweat sodium varies roughly from 20 to 80 mmol/L (about 460–1,840 mg/L), so the Standard tier replaces about half of a typical loss at matched volumes. The tiers are starting points, not prescriptions.

sodium budget = target mg/L × litres − alginate sodium; salt share = 25% when enabled; citrate = remainder ÷ 234.5 mg/g

Sodium citrate is the default source. For the same sodium it dissolves into about a third fewer particles than table salt (a 500 mg/L target costs roughly 29 mOsm/kg as citrate against 43 as salt), tastes salty-sour rather than briny, and keeps the bottle slightly alkaline, which suits the hydrogel agents. Its trade-offs are stated in the app: no chloride, 1.7 times the powder mass of salt for the same sodium, and a mild laxative effect at several grams, so the input limit is 5 g per bottle. Table salt is optional; when enabled it takes about a quarter of the budget and citrate gives way. Suggested grams are rounded to 0.1 g.

Custom recipes estimate sodium from table salt at 393.4 mg/g, trisodium citrate dihydrate at 234.5 mg/g and sodium alginate at a nominal 116 mg/g. Check the product label or certificate when alginate sodium matters because grades vary.

Hydrogel texture agents

Sodium alginate and citrus pectin are suggested at 1.2 and 0.8 g per litre of water, 0.2% of the water weight in total. That is the proportion used in the Maurten-supplied research beverages (Sutehall et al., 2020 and 2022), applied at both 10% and 26% carbohydrate, and it is consistent with the 83 g sachet that carries 80 g of carbohydrate in Drink Mix 320. The Maurten-inspired preset uses the same 0.6 g and 0.4 g per 500 mL, attributed to that research rather than to the label.

The gel forms when the drink meets stomach acid, so the bottle must stay near neutral pH: no citric acid, fruit juice or effervescent electrolyte tabs. Sodium citrate helps here because it is alkaline and binds some of the calcium in hard water, which would otherwise cross-link the alginate early; soft or filtered water avoids the problem. Use food-grade, low-to-medium viscosity sodium alginate and pure citrus pectin, not jam-setting pectin with added acid, sugar or calcium, and blend the dry powders before adding water so the alginate does not clump. Maurten also warns that dissolved electrolytes compete with alginate cross-linking; its own research beverages still carried 1.5 g/L of salt, so the Standard and Heavy tiers are within what was tested.

The evidence is neutral and the app says so. At rest, an 18% carbohydrate drink with alginate and pectin emptied from the stomach faster in its first half hour. In running trials at 60–71% of maximal oxygen uptake (McCubbin et al., 2020; Barber et al., 2020; Sutehall et al., 2022) adding them changed neither gastrointestinal symptoms, carbohydrate oxidation nor blood glucose, and two studies recorded higher stomach fullness. The 2022 meta-analysis (Mears et al.) found no performance, oxidation or glucose benefit and noted that most trials were too gentle to provoke gut trouble in the control arm. Mix My Bottle makes no claim that a homemade gel behaves like a branded hydrogel, or that it reduces sloshing.

Concentration, intake and stomach comfort

Drinks above 8 g carbohydrate per 100 mL are marked as concentrated fuel and need a separate fluid plan. The app gives context around the common 30–60 g/h range for exercise lasting about 1–2.5 hours and up to 90 g/h for longer efforts using multiple transportable carbohydrates. It does not present higher intake as established guidance.

Fluid sits in the stomach longer when the drink is concentrated, when the effort is hard (above roughly 70–75% of maximal oxygen uptake) and when large volumes are swallowed at once. The guide therefore suggests keeping fuel bottles at or below 8 g per 100 mL unless the gut has been trained for more, sipping 150–250 mL every 15–20 minutes rather than half a bottle at once, and pairing a concentrated bottle with plain water. Sodium with glucose speeds water absorption in the small intestine, which is the main reason a fuel bottle carries sodium at all.

Sodium checks: values below 230 mg/L, or above the roughly 460–920 mg/L that commercial mixes deliver, are shown as warnings. Values between 690 and 920 mg/L receive an information note instead, because several commercial mixes sit there. The default 750 mL, 60 g, Standard-tier bottle starts with no warnings.

Commercial-inspired presets

Tailwind, Maurten 320 and INFINIT Premium Fructose Fuel names identify the product style being referenced. Published label facts are kept separate from illustrative ingredient allocations. Exact formulations, flavourings, salt and bicarbonate quantities and manufacturing methods are proprietary and may change. The Maurten-inspired preset's 0.6 g alginate and 0.4 g pectin per 500 mL come from the published research beverages, not from the label.

Commercial preset osmolality values use only the ingredient quantities shown. They are labelled carbohydrate-only where undisclosed electrolyte or hydrocolloid weights prevent a complete estimate. None of the presets is a product replica or endorsed substitute.