Calorie Maintenance Calculator

Enter your stats once and get five numbers that actually matter: calories, macros, body fat estimate, fiber target, and daily water. No signup, no ads, just the math.

How to actually use these numbers

A calculator is only useful if you know what to do with what it tells you. Here’s a plain-language breakdown of each number above, where it comes from, and where it falls short.

Your calorie numbers aren’t a verdict, they’re a starting point

The three calorie figures above (maintain, deficit, surplus) come from the Mifflin-St Jeor equation, which estimates your basal metabolic rate from your height, weight, age, and sex, then multiplies it by an activity factor. This is the same formula most registered dietitians use as a baseline, and it’s considered more accurate than the older Harris-Benedict equation that a lot of older calculators still rely on.

That said, it’s an estimate, not a measurement. Two people with identical stats can have meaningfully different metabolisms due to genetics, muscle mass, hormone levels, or medication. Think of the number as a reasonable place to start, not a fixed target. If you track your actual intake and weight for two to three weeks and the result doesn’t match the prediction, trust your own data over the formula.

The 15% deficit and surplus figures are deliberately moderate. Aggressive deficits (25% or more below maintenance) tend to backfire over time: they’re harder to sustain, often lead to more muscle loss alongside fat loss, and can trigger the kind of restrict-then-binge cycle that makes long-term progress harder, not easier. A smaller, sustainable gap tends to produce better results over months, even if it feels slower week to week.

Why the macro split is 30/40/30, and when to change it

The default split, 30% protein, 40% carbs, 30% fat, is a reasonable general-purpose starting point for most adults who are moderately active and have no specific medical condition. It’s not the only valid way to eat.

A few situations where you might reasonably deviate:

• Endurance athletes training many hours a week often do better with a higher carb percentage, since carbohydrates are the body’s preferred fuel for sustained aerobic effort.
• Strength training with a fat loss goal sometimes calls for a slightly higher protein percentage, since protein helps preserve muscle mass during a calorie deficit.
• Certain medical conditions, like type 2 diabetes or PCOS, are sometimes managed with a lower-carb approach under a doctor’s or dietitian’s supervision. That’s a clinical decision, not a default setting.

If you’re generally healthy and just want a sustainable, balanced way to eat, the default split is a sensible place to stay.

The body fat estimate is a tape measure, not a lab test

The body fat percentage above uses the U.S. Navy method, which estimates body fat from waist, neck, and (for women) hip measurements. It was originally developed for quick field assessments, not precision diagnostics.

It’s reasonably useful for tracking your own trend over time, since the same measuring technique applied consistently will show you real direction of change. It’s considerably less reliable as an absolute number, especially for people with body types that don’t match the average build the formula was calibrated on, including very muscular or very lean individuals. If you need a clinically accurate number, options like DEXA scans, hydrostatic weighing, or BodPod testing are far more precise, though also more expensive and less convenient.

A practical tip for measuring: wrap the tape snugly but not tight, measure at the navel for waist and just below the larynx for neck, and take the measurement at the same time of day (ideally morning, before eating) for consistency.

Fiber: the nutrient almost everyone is short on

The fiber target shown is based on standard age and sex-based recommendations, generally 38 grams a day for younger men, 30 grams for older men, 25 grams for younger women, and 21 grams for older women. Most people eating a typical Western diet get well under half of this.

Fiber matters more than its quiet reputation suggests. It feeds the bacteria in your gut that produce short-chain fatty acids linked to lower inflammation, it slows digestion in a way that helps regulate blood sugar and appetite, and it’s one of the most consistently supported dietary factors in reducing long-term colon cancer risk.

The practical way to close the gap isn’t usually a fiber supplement, it’s structural: a serving of beans or lentils most days, fruit with the skin on, whole grains instead of refined ones, and vegetables at more than one meal a day. If you’re currently eating very little fiber, increase it gradually over a couple of weeks. A sudden jump can cause bloating and discomfort that has nothing to do with anything being wrong, just your gut adjusting to more material to process.

Water needs are more individual than the number suggests

The water target above starts from a baseline of roughly 33 milliliters per kilogram of body weight, then adds a bonus scaled to your activity level. This is a commonly used general guideline, not a fixed medical requirement.

Real water needs shift with climate, altitude, sweat rate, and overall health, and some medical conditions change the calculus entirely, including kidney disease and certain heart conditions, where more water is not automatically better. A simpler, low-effort gauge for most healthy people: pale yellow urine throughout the day generally indicates adequate hydration, while dark yellow suggests you should drink more. If you have a kidney, heart, or liver condition, follow your doctor’s guidance over any general calculator.

What this tool isn’t

These five numbers are a reasonable starting framework, not a substitute for individualized care. If you have a diagnosed medical condition, a history of disordered eating, or you’re pregnant or breastfeeding, the general formulas above may not apply to you the same way they apply to a general healthy adult population. A registered dietitian or your physician can tailor these numbers to your specific situation in a way no calculator can.

Used as intended, treat these figures as a place to start a conversation with yourself about your habits, not a strict set of rules to follow to the gram.