Hydration Status

Your body is a continuous energy system: energy stored in food minus energy expended through metabolism and activity determines whether stores grow, shrink, or hold steady. The classic model assumes 3,500 kcal ≈ 0.45 kg (1 lb) of body fat — a useful shorthand for planning, though real-world weight change slows as body mass drops (smaller bodies need fewer calories).

Start with BMR — the energy you use at complete rest. Mifflin–St Jeor (1990) is a solid default from height, weight, age, and sex; Katch–McArdle improves accuracy when you know lean body mass (it tends to be more accurate for lean or athletic people). Multiply BMR by an Activity Factor (PAL) to get TDEE:

1. Sedentary (1.2) — desk job, little exercise.
2. Lightly active (1.375) — 1–3 light sessions/week.
3. Moderately active (1.55) — 3–5 sessions/week.
4. Very active (1.725) — 6–7 hard sessions/week.
5. Athlete-level (1.9) — twice-daily or physical labor + training.

To lose weight, a sustained deficit of 500–750 kcal/day is a common target for ~0.5–0.75 kg/week early on — rapid cuts raise muscle-loss and rebound risk. To build muscle, a surplus of 250–500 kcal/day paired with resistance training limits unnecessary fat gain. Maintenance means matching TDEE closely and adjusting based on 2–4 weeks of trend data, not daily fluctuations.

NEAT (non-exercise movement — steps, posture, fidgeting) and TDEA (total daily energy expenditure via activity) explain why two people with identical BMR and exercise can differ by 300–600 kcal/day in real expenditure. Track steps and daily activity, not just workouts.

Three macronutrients supply energy: protein and carbohydrate provide ~4 kcal/g each, fat provides ~9 kcal/g, and alcohol provides ~7 kcal/g (with no essential nutrients). Splitting your target between them is a design choice, not a rule of thumb — but sensible ranges exist.

• Protein — 1.6–2.2 g/kg/day supports muscle retention during a deficit or growth during a surplus (higher ranges matter more under heavy training). 0.8 g/kg/day is the classic RDA for sedentary adults.
• Fat — typically 0.6–1.0 g/kg/day, or ~20–35% of calories; essential fatty acid needs set a practical floor below which hormones and absorption suffer.
• Carbohydrate — fills the remainder and fuels high-intensity training; endurance athletes often target higher intakes (5–8 g/kg/day) around training loads.

Micronutrients (vitamins, minerals) do not supply energy but enable every metabolic process. Common targets: fiber 25–35 g/day, sodium < 2,300 mg/day, plus adequate potassium, magnesium, iron, calcium, and vitamin D (individual needs vary with age, sex, and lab values). Food-first sources generally beat supplements when variety is achievable.

Water needs depend on body size, climate, and activity — a practical baseline is roughly 30–40 mL/kg/day (about 2.1–2.8 L for a 70 kg person) with substantial increases for sweat losses. For prolonged exercise, add 400–800 mL/hour and consider electrolytes (sodium ~300–600 mg/L of sweat) for sessions beyond ~60–90 minutes, especially in heat.

To evaluate exercise you need intensity, duration, and frequency. Three systems do the work.

MET (Metabolic Equivalent of Task) standardizes intensity: 1 MET ≈ resting oxygen consumption (~3.5 mL O₂/kg/min). MET minutes = MET value × duration (minutes). Brisk walking ≈ 3.5–4 METs; running ≈ 8–12+ METs depending on pace. Public-health guidance commonly translates to 150–300 minutes of moderate-intensity or 75–150 minutes of vigorous-intensity activity per week (WHO), plus muscle-strengthening 2+ days/week. MET minutes make it easy to sum across activities and compare days.

Heart-rate zones use training intensity relative to a maximum heart rate. The simple estimate is 220 − age, but individual variation is wide (±10–15 bpm), so using measured max (from a graded test) or heart-rate reserve (Karvonen method: target HR = resting HR + intensity × (max − resting)) gives better zones. Typical bands:

1. Zone 1 (50–60% max) — warm-up, recovery.
2. Zone 2 (60–70%) — endurance base, fat oxidation.
3. Zone 3 (70–80%) — tempo, aerobic efficiency.
4. Zone 4 (80–90%) — threshold, lactate accumulation.
5. Zone 5 (90–100%) — VO₂max intervals, all-out.

VO₂max is maximal oxygen uptake (mL/kg/min) — a gold-standard aerobic fitness measure. Submaximal estimators (from heart rate, pace, and grade) give useful approximations; lab testing with gas analysis is more precise. VO₂max generally improves with consistent aerobic training and declines with age (~5–10% per decade after ~30, faster without training).

Recovery and training load tools (e.g. training impulse, recovery HR) estimate cumulative stress. A heart rate that stays elevated long after stopping exercise, or a resting HR that climbs week-over-week, often signals inadequate recovery — sleep, nutrition, or intensity management.

The Hydration Status is a free health assessment tool free hydration status — essential health assessment tool for. It uses clinically validated formulas and medical research to provide personalized health metrics based on your inputs. By entering simple measurements like your age, weight, height, and other relevant data, you receive instant insights into various aspects of your health and fitness. This tool is ideal for tracking progress toward wellness goals, understanding important health indicators, and making informed decisions about your lifestyle. Always consult a healthcare professional for medical advice, but use the Hydration Status as a reliable reference point on your health journey.

The Hydration Status provides evidence-based health metrics to help you understand and track your wellness. Use it alongside professional medical advice for a clearer picture of your health status.

Using the Hydration Status is quick and easy. Begin by entering your basic health metrics such as age, gender, height, weight, and any other requested measurements. The calculator processes your inputs using validated health formulas and displays your results instantly. You can adjust your inputs to see how different values affect your health indicators. Use the results section to understand what your numbers mean and track changes over time by saving or noting your results. Hydration Status: always consult with a healthcare professional before making health decisions based on calculator results.

The formula used by the Hydration Status is:

The Hydration Status uses validated formulas that follow industry standards and academic best practices for health calculations.

Understanding the formula behind the Hydration Status helps you interpret the results more effectively. Each variable in the formula represents a specific input that you provide, and the calculator handles the complex arithmetic automatically.

Key references for this formula

• World Health Organization (WHO, 2020). Guidelines on physical activity and sedentary behaviour. ↗
• Mifflin M. D. et al. (1990). A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr, 51(2), 241–247. ↗
• U.S. Department of Agriculture / U.S. Department of Health and Human Services. Dietary Guidelines for Americans, 2020–2025. ↗