Swim Nutrition Calculator
The formula
What the carb periodisation tells you
The swim-fuel arithmetic adapted from endurance-sport carbohydrate tiers: grams per kilogram matched to the day’s session count and intensity.
Calculation: Carbs = g/kg tier (3/5/8) × kg; in-session 30–60–90 g/h by duration. Enter your inputs and every substitution is shown below the result.
Reading the result
Easy technique days at 3 g/kg teach the gut to use fat; race-pace double days at 8 g/kg keep the glycolytic system trainable.
Rules of thumb: Elite swim squads periodise 3–10 g/kg/day across the microcycle
Limitations and best practice
The 30–60–90 g/h in-session ladder assumes practiced gut tolerance — build it in weeks, not on championship morning.
This calculator gives an estimate based on standard formulas; it is not professional financial, medical, legal or engineering advice. Verify anything you plan to act on with a qualified professional and your own records.
Frequently asked questions
Swim fasted?
Why carbs in the pool at all?
Source & methodology
Burke/IJSNEM carbohydrate availability guidelines.
How Swim Nutrition works — and what your result really means
This page was written for one job: turning your own inputs into a defensible figure, with the working shown. Swim Nutrition is the kind of number people argue about from memory. This page ends that argument with arithmetic you can watch happen: enter your figures, get Daily carbohydrate in real time, and see every substitution printed below.
Most confusion about Swim Nutrition comes from mixing up the input you control with the input you merely observe. The formula treats them identically, but your decisions should not: one deserves measurement, the other deserves a defensible estimate.
People rarely disagree about arithmetic; they disagree about assumptions that were never written down. Printing the substitution and the sensitivity ranking removes that category of disagreement for Swim Nutrition.
Every figure in the prose is generated by the engine rather than written beside it — the worked example resolves to daily carbohydrate = 525 g on the default inputs, and the sensitivity section ranks the inputs that move the result — Weight first, at ≈10.0 % of the headline for a ten-percent error either way in that input. Work down the page and by the end you could re-derive the result in a spreadsheet from memory.
The Swim Nutrition formula, explained
Here is the complete model this tool runs — Carbs = g/kg tier (3/5/8) × kg; in-session 30–60–90 g/h by duration — with each input explained below. If a competitor’s page gives you a different answer from the same inputs, this is the text that settles which of you is right.
Weight (kg) (example value 105) is a plain measured quantity — the unit shown in the label is the unit the formula expects. Weigh rather than estimate where you can — this field usually enters the formula multiplicatively.
Session length (min) (example value 90) is a plain measured quantity — the unit shown in the label is the unit the formula expects. Small measurement errors grow here: a length that is squared or cubed in the model magnifies a one-percent slip into a three-percent answer.
Intensity (example value Aerobic build) is a selector, not a measurement: the engine follows a different route for each option. Replace the example with the figure from your own records — the tool recomputes instantly and the printed steps follow your numbers.
Sessions per day (example value 1) is a plain measured quantity — the unit shown in the label is the unit the formula expects. If the period is partial, decide whether you mean elapsed or planned time and keep that meaning across every field.
What each “Intensity” choice actually does: Technique/easy → 315 g · Aerobic build → 525 g · Race-pace set → 840 g That table is the honest answer to “does this option matter”, re-derived from the formula rather than hard-coded into page copy.
The default Swim Nutrition calculation, written out in full
Rather than describe the calculation, here it is end to end — every substitution in order, starting from the inputs above. Starting figures: Weight (kg), Session length (min), Intensity, Sessions per day. The computed daily carbohydrate comes out at 525 g, which the interpretation band labels “A 90-min aerobic session asks for 5 g/kg/day — 525 g total across 1 session(s), with ~90 g inside the workout once it runs past the hour”.
- Tier by intensity: 5 g/kg
- 5 × 105 × 1 = 525 g
- In-session: 60 g/h × 1.50 h = 90 g
Target per kg — 5 g/kg. If your inputs change, this is usually the first companion figure to move.
In-session carbs — 90 g. This is the number experienced users quote when the headline alone would mislead.
Protein anchor — 158 g/day. Read next to the headline, this is the figure that shows the shape of the trade-off.
Recovery window slot — 1:0.75 carb:protein within 45 min. This is the number experienced users quote when the headline alone would mislead.
Keep this worked example open while you enter your own figures: matching the shape of the substitution is the fastest way to spot a unit or convention mistake.
Scenario table: Swim Nutrition at ±10 % and ±20 % of the key input
Read this table as the practical error bar on the headline figure. It answers the question people actually have after seeing a single number: how wrong could this be if the main input is off by ten or twenty percent?
| Weight setting | Daily carbohydrate |
|---|---|
| 80 % of the example value | 420 g |
| 90 % of the example value | 473 g |
| example inputs | 525 g |
| 110 % of the example value | 578 g |
| 120 % of the example value | 630 g |
The corridor runs from 420 g to 630 g across that band — which is the range worth planning inside rather than the single 525 g point estimate. Reproduce it in the form above by editing Weight alone; the substitution steps will follow your figures exactly.
The levers behind Swim Nutrition, ranked by effect
Nobody should have to guess which input matters. The engine was re-run once per field below — ten percent up, ten percent down, everything else frozen — and the results ranked by how far they moved the daily carbohydrate. For Swim Nutrition the ranking is measured rather than guessed, and it belongs to these defaults: shift the starting point and the order can shift with it.
- Weight: ten percent up gives 578 g, ten percent down gives 473 g — ≈10.0 % of the daily carbohydrate either way
- Sessions per day +10 % → Swim Nutrition = 578 g · −10 % → 473 g (the daily carbohydrate shifts ≈10.0 %)
Weight is the dominant lever here: ten percent either way moves the result by about 10.0 %, from 473 g to 578 g. Measure that input from a document rather than from memory, and Sessions per day is effectively tied with it (≈10.0 % for the same nudge), so verify the pair together. Everything below that can stay approximate, which is a licence to stop chasing data that would not change the decision.
What a Swim Nutrition of 525 g means in practice
The value above only becomes useful the moment you know what it is being measured against. The verdict attached to the default calculation — “A 90-min aerobic session asks for 5 g/kg/day — 525 g total across 1 session(s), with ~90 g inside the workout once it runs past the hour” — is one band on a ladder your own figure may sit somewhere else on. Before treating the band as fact, note its width: ten percent either way on Weight already spans 473 g to 578 g. The practical reading rules: compare against your own history before comparing against other people; treat band boundaries as zones, not walls — one point on the wrong side of a threshold rarely changes a real outcome; and when a companion output contradicts the headline, believe the pair.
Placing this figure in context: calculators of this kind differ less in arithmetic than in what they choose to ignore. This one keeps Weight (kg) explicit so that the omissions are visible rather than hidden in a preset.
Common mistakes with Swim Nutrition (and the fix)
The 30–60–90 g/h in-session ladder assumes practiced gut tolerance — build it in weeks, not on championship morning. This calculator gives an estimate based on standard formulas; it is not professional financial, medical, legal or engineering advice. Verify anything you plan to act on with a qualified professional and your own records.
Comparing a Swim Nutrition computed here with a figure from another source that uses different conventions. Same name, different denominator — the disagreement is usually in the definitions, not the data.
This model has its own particular trap: Weight carries ≈10.0 % of the response per ten percent of error, so effort spent elsewhere is largely decorative.
The subtlest error is answering the wrong question precisely. Confirm that daily carbohydrate is actually the quantity your decision needs — the arithmetic is flawless either way, which is what makes the mistake invisible.
Before you trust your Swim Nutrition: a short checklist
- Compare the result with one independent method or published benchmark.
- State, in one sentence, which convention each rate, unit or period in the form is using.
- Put Weight under a magnifier; the sensitivity table above is the reason why.
- Recompute once with the dominant input deliberately set low, and see whether the decision changes.
- Check that every field the formula needs actually arrived from a document, not from recollection.
- Run the ±10 % stress on the top two levers and check that your conclusion survives both.
Step by step: getting a trustworthy Swim Nutrition out of this tool
Using a calculator well sounds trivial, but the difference between a decision-grade figure and a throwaway one lives entirely in the routine. The routine for Swim Nutrition takes a minute to learn and applies to every input above.
Step 1 — start from evidence. The inputs behind Swim Nutrition are weight (kg), session length (min), intensity, sessions per day. Write them down with their source next to each one; if you cannot name where a figure came from, that is the input most likely to be wrong. A result worth acting on survives having its two shakiest inputs halved.
Step 2 — start from the case you can defend. Enter pessimistic-but-honest figures first; the optimistic run is a ceiling, not a plan. A conclusion that holds on conservative inputs holds everywhere. Suspiciously tidy answers deserve the same scrutiny as untidy ones.
Step 3 — measure what deserves measuring. The ranked levers above tell you where a careful figure pays off. Everything else can stay approximate, which is a licence to stop hunting for data you do not need. If a result feels obviously right, that is the moment to check the inputs hardest.
Step 4 — stress before you commit. A decision that survives a ten-percent squeeze on its two biggest inputs needs no luck to be sound. One that does not survive is a decision about hope, not about arithmetic. Precision is a promise you make about your data; make sure your inputs can keep it.
Step 5 — write the one-line memo. “Daily carbohydrate = 525 g on this date, from these inputs.” That line is the entire deliverable; everything else on this page is how you earned the right to write it. The test of a good estimate is not that it feels right but that it changes what you do.
From calculation to decision: where Swim Nutrition earns its keep
In Swimming the figure computed here is usually the first one somebody asks to see. Having it — with the formula behind it — changes your position in the conversation from participant to reference. Rounding early is the quietest way to introduce a permanent error.
Used properly this is a five-minute filter that saves weeks. Compute Swim Nutrition, reject what fails, and only then bring in the expensive analysis for the survivors. A figure nobody can reproduce is a figure nobody will act on twice.
Nothing here is stored or transmitted, so the habit of checking is free: open the page, re-enter current figures, compare with the number you saved last time. Comparisons are cheap: run the identical calculation for the alternative and look at the gap.
Quick answers: what searchers ask about Swim Nutrition
What affects Swim Nutrition the most?
Measured on this engine, Weight is the dominant lever: moving it ±10 % shifts the daily carbohydrate across 473 g to 578 g — about 10.0 % of the headline, with Sessions per day next at ≈10.0 %. The ranked list in the sensitivity section is computed live, not asserted from a template.
Do sessions per day and weight matter equally?
Effectively. Measured on this engine they land at ≈10.0 % and ≈10.0 % for the same ten-percent nudge, so the honest advice is to get both right; chasing precision in only one of them buys almost nothing.
How much does the “Intensity” choice change the answer?
A great deal, on these inputs: Swim Nutrition comes out at 315 g on the lowest option (“Technique/easy”) and 840 g on the highest (“Race-pace set”). Each option is listed with its computed value so you can see what the choice is worth before you make it.
What is a typical Swim Nutrition?
With the example inputs on this page the result is 525 g, labelled “A 90-min aerobic session asks for 5 g/kg/day — 525 g total across 1 session(s), with ~90 g inside the workout once it runs past the hour”. “Typical” varies with situation, which is why every result here ships with its verdict band and its sensitivity list: they turn one figure into a range you can locate yourself inside.
How do I calculate Swim Nutrition by hand?
Use the stated model — Carbs = g/kg tier (3/5/8) × kg; in-session 30–60–90 g/h by duration — and substitute in the order the tool prints (it starts from Tier by intensity: 5 g/kg). On the example inputs the hand route lands on 525 g, exactly what the calculator shows. A spreadsheet reproduces it in two or three cells; doing it once by hand is what makes the automated answer trustworthy.
What happens to Swim Nutrition if weight changes by 10 %?
The engine was re-run with that field moved by ten percent while everything else stayed fixed: the daily carbohydrate goes across 473 g to 578 g, a swing of roughly 10.0 % around the 525 g baseline. That ratio is the practical definition of how much this input matters.
Is the Swim Nutrition result of 525 g good or bad?
Neither, on its own — the label “A 90-min aerobic session asks for 5 g/kg/day — 525 g total across 1 session(s), with ~90 g inside the workout once it runs past the hour” is the band this figure falls in for the example inputs, and your own inputs will place you elsewhere on the same ladder. Judge the number against your history and your alternatives, and remember that a ten-percent error in Weight alone moves it by ≈10.0 %.
How often should I check Swim Nutrition?
Whenever an input changes by more than a few percent, and otherwise on the rhythm of your decisions — before a purchase, a review, a renewal. Swim Nutrition is a snapshot, not a subscription; stale snapshots are the most common silent error in Fitness & Sports planning.
Can Swim Nutrition be negative or empty?
Yes, and that is informative rather than broken: a negative Swim Nutrition usually means the inputs encode an outflow or a shortfall, and the verdict band above labels exactly that situation instead of hiding it.
Swim fasted?
Only on technique days and only if the session is genuinely easy — fasted race-pace work just makes ugly pace.
Why carbs in the pool at all?
Water drains the gut slower and brain-on-tempo work is glucose-hungry past ~75 minutes.
Is my data private on this page?
Yes — computation happens locally in your browser, with no account, no tracking of your inputs and nothing sent to a server. The printed formula is the whole story of what happens to your figures.
What the labels on this page mean
- Target per kg
- 5 g/kg on the example inputs — a companion figure printed beside the headline of Swim Nutrition so that no result is read in isolation.
- In-session carbs
- 90 g for the Swim Nutrition worked case; it sits next to the main result because it carries context the headline leaves out.
- Protein anchor
- 158 g/day in the default Swim Nutrition calculation — one of the secondary figures an experienced reader checks before trusting the primary number.
- Daily carbohydrate
- The primary output of this tool: 525 g for the default inputs, computed exactly from Carbs = g/kg tier (3/5/8) × kg; in-session 30–60–90 g/h by duration.
- Worked example
- The calculation written out in full so that nothing on this page has to be taken on trust.
- Verdict band
- A named zone on the range of plausible results; the example inputs land in “A 90-min aerobic session asks for 5 g/kg/day — 525 g total across 1 session(s), with ~90 g inside the workout once it runs past the hour”, and your inputs may not.
- Sensitivity (±10 %)
- How far the Swim Nutrition moves when a single input is nudged ten percent either way; the ranked list on this page is computed live from this engine.
The provenance of this Swim Nutrition calculation
Everything above runs on one stated formula, applied without hidden coefficients: Carbs = g/kg tier (3/5/8) × kg; in-session 30–60–90 g/h by duration. Source of record: Burke/IJSNEM carbohydrate availability guidelines. Where a professional version of this calculation differs, it differs in inputs and jurisdiction-specific coefficients, not in the algebra — which is why re-checking your inputs beats hunting for a second calculator.
Treat the output as a precise answer to the question you typed: exact arithmetic, transparent formula, published source, no hidden rounding. What that buys you is reproducibility — two people, two browsers, the same arithmetic, and a printed trail from inputs to result that either of them can audit.
After the number: what to do with it
Re-run the calculation with your own figures, stress the two most sensitive inputs by ±10 %, and only then act on the result.
Whoever you are (people who need one trustworthy number before their next decision), the next step is the same: replace the example inputs with your own, note the date, and re-run whenever a figure moves. In Fitness & Sports, a dated figure is a trend, and an undated one is a rumour.