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Calculators that show their work.
Every sports nutrition calculator on the internet hands you a number. Almost none of them tell you which equation produced it, which position stand the ranges came from, or how wrong it could reasonably be. These four do.
Calories & macros
Daily energy, protein, carbohydrate and fat from your training load — plus an energy availability check most calculators skip.
02Sweat rate & hydration
Measure your real sweat rate from a weigh-in, then get fluid and sodium targets for the session in front of you.
03Protein timing
Your daily total split into doses that actually clear the threshold, laid out across your waking hours.
04Carb loading & race fueling
Loading grams, the pre-race meal, grams per hour while you are moving, and what to replace afterwards.
Why I built these
I am a registered dietitian, and a large part of my job is having the same conversation repeatedly: someone arrives with a number they got from a website, the number is wrong for them, and there is no way to work out why because the website never said what it was doing. Sometimes it used a general-population equation on a very muscular person. Sometimes it assumed a training load that has nothing to do with what they actually do. Sometimes it just made the number up.
So these calculators are built the other way round. Each one names the equation, links the paper, shows your result as a position inside the published range rather than as a lone figure, and tells you when your inputs produce something that does not add up. When your calorie target cannot accommodate the carbohydrate your training load calls for, it says so, because that conflict is usually the most useful thing you could learn that day.
The short version
A calculator can give you a decent starting estimate. It cannot know your metabolism, your history, your sleep, your stress, or the fact that you always underestimate how hard you train. Use the number as a place to start, then adjust based on what actually happens over the next fortnight. That is how it works in clinic too.
What these will not do
They will not diagnose anything, they will not replace working with a dietitian who can see your whole picture, and they are not medical nutrition therapy. If you are managing a medical condition, if you are pregnant, if you have any history of disordered eating, or if you are an adolescent athlete, the right move is a conversation with a person rather than a form on a webpage.
They also will not remember you. There are no accounts, no email capture, and no analytics tracking your inputs. Every calculation runs in your browser and the numbers you type are gone the moment you close the tab. That is a deliberate design choice — health data that never leaves your device cannot be leaked, sold or subpoenaed.
How accurate is any of this?
More honest than most sites will tell you: prediction equations for resting metabolic rate typically land within about ten percent of a measured value for most people, which on a 2,400 calorie estimate is a spread of roughly 240 calories in either direction. Activity multipliers are cruder still. Every guideline range you see here exists because the research produced a range, not a point.
That is not a reason to ignore the numbers. It is a reason to treat them as a starting hypothesis you test over two to three weeks, which is exactly what the methods page walks through. A good estimate plus honest self-monitoring beats a precise-looking number every time.