Health
BMI, calorie & wellness calculators
Health calculators
20 tools for BMI, Calorie needs, Due date and more — accurate, instant, and free.
Reckonist’s Health calculators turn everyday wellness questions into clear numbers — your BMI and what it means, daily calorie and macro needs, a pregnancy due date, and body-fat and ideal-weight ranges. Each one runs on recognised clinical formulas, free and with no sign-up, computing in your browser so your figures never leave your device.
Clinical & labs7
A1C Calculator
A1C ↔ eAG, GMI from CGM, IFCC mmol/mol and the ADA category — a screening estimate.
eGFR Calculator
CKD-EPI 2021 race-free eGFR from creatinine, age and sex, with the KDIGO stage — a screening estimate.
BAC Calculator
Widmark blood-alcohol estimate + time-to-sober + per-state DUI limits — an estimate only, never a clearance to drive.
Cholesterol Ratio Calculator
TC/HDL, LDL/HDL, TG/HDL and non-HDL with risk bands, the TG/HDL insulin-resistance flag and Friedewald LDL — risk markers, not a diagnosis.
Creatinine Clearance Calculator
Cockcroft-Gault creatinine clearance for renal drug dosing, with ideal/adjusted body weight and the CrCl-vs-eGFR distinction — an estimate for dose adjustment, not dosing advice.
Anion Gap Calculator
Anion gap = Na − (Cl + HCO₃), with the albumin-corrected (Figge) gap that unmasks a hidden acidosis and the delta gap for mixed disorders — an interpretation aid, not a diagnosis.
Body Surface Area Calculator
BSA in m² by five formulas — Mosteller, Du Bois, Haycock, Gehan-George and Boyd — shown side by side, with the 2.0 m² chemo dosing cap. An estimate; clinical/chemo dosing must be clinically verified.
Energy & nutrition4
TDEE Calculator
BMR by Mifflin-St Jeor, Harris-Benedict or Katch-McArdle × an activity factor → TDEE, plus goal calories for cut/maintain/bulk. A fitness estimate — the activity factor is the biggest variance.
Macro Calculator
Protein-first macros on the TDEE engine: protein set by bodyweight (g/lb by goal), then carbs & fat split by diet preset (balanced/low-carb/keto/high-protein/Zone). Grams + % + per-meal, reconciled 4/4/9. A fitness estimate, not dietary advice.
Protein Intake Calculator
How much protein per day, as an evidence-based range by goal (RDA/maintain/muscle/fat-loss) and population (general/older/pregnant) — set on bodyweight or lean mass. Per-meal ≈ 0.4 g/kg for MPS; flags the "1 g/lb" myth. A fitness estimate, not medical advice.
Weight-Loss Percentage Calculator
Track weight-loss as a % of your starting weight, with a weekly-rate traffic light (safe ≈ 0.5–1%/week) and the clinical 5%/10% milestones — ≥5% loss is associated with HbA1c ↓0.6–1.0% (ADA / ACC-AHA-TOS). Associations, not guarantees; not medical advice.
Fitness & training5
Running Pace Calculator
Solve pace, time or distance from the other two (km/mi), then predict your 5K/10K/half/marathon times from a recent race with the Riegel formula (T2 = T1 × (D2/D1)^1.06). Even splits + treadmill pace. A fitness estimate — reliable to the half, optimistic beyond.
One-Rep Max Calculator
Estimate your 1RM from weight × near-failure reps with three formulas (Epley, Brzycki, Lombardi) averaged into one number — Epley is excluded at ≤2 reps because it reads ~3% high at 1 rep — plus a rep-max % training table (loads for 1–12 reps) and per-lift pages. A fitness estimate; accuracy degrades above ~10 reps.
Heart Rate Zone Calculator
Estimate your max HR with the research-validated Tanaka formula (208 − 0.7 × age) — more accurate than the age-biased 220 − age — then get five training zones with %HRmax and Karvonen (%HRR) shown side by side (~20 bpm apart, the #1 zone error) and Zone 2 highlighted. A fitness estimate (±10–12 bpm); a lab test or wearable is most accurate.
Calories Burned Calculator
Estimate calories burned from activity (MET) × body weight × duration, with the 2024 Adult Compendium MET table and per-activity presets (walking/running/cycling). A net-vs-gross toggle (gross includes resting metabolism; net subtracts ~1 MET — the honest figure for weight loss). A steady-state estimate — the MET model ignores EPOC/afterburn; a wearable is more personalised.
VO2 Max Calculator
Estimate VO₂ max (ml/kg/min) from a field test — the Cooper 12-minute run ((distance_m − 504.9) / 44.73), the Rockport 1-mile walk (time + ending HR + weight), or the Uth resting-HR ratio (15 × max HR / resting HR) — then read it against age/sex Cooper/ACSM fitness norms. When the Uth max HR is unmeasured we substitute Tanaka (208 − 0.7 × age) and flag the chained estimate. A field estimate, not a lab VO₂ max; general fitness guidance.
Body & wellness4
Water Intake Calculator
Set a daily water target from your body weight (≈ 33 mL/kg — the 30–35 mL/kg bodyweight method), plus activity (≈ 12 mL per exercise minute) and a hot/humid climate uplift (+15%), shown in mL, litres and fl oz with a base/activity/climate breakdown. Busts the "8 glasses a day" myth (needs scale with weight, activity and climate) and adds NASEM total-vs-beverage context (~20% of water comes from food, so their ~3.7 L men / 2.7 L women totals look larger). General hydration guidance, not medical advice — the real check is pale-straw urine and drinking to thirst.
Intermittent Fasting Calculator
Schedule your intermittent fasting windows from a protocol (16:8 / 18:6 / 20:4 / OMAD) and your last-meal time — the eating window opens the fasting-hours later and closes at the next last-meal time, shown as exact clock times (last meal 8:00 PM on 16:8 → eat 12:00 PM–8:00 PM). Overlays an approximate fasting-state timeline (fed <12h · glycogen depleting 12–16h · mild ketosis 16–24h · deeper ketosis + autophagy 24h+), plus honest "what breaks a fast" guidance (black coffee/water/electrolytes fine; cream/sugar/sweeteners/BCAAs break it). Prominent safety screen: not without a clinician for Type 1 diabetes or insulin/sulfonylureas (hypoglycemia), pregnancy or breastfeeding, a history of eating disorders, or children and adolescents. Lifestyle information, not medical advice.
Body Fat Calculator
Estimate body-fat % three ways — US Navy (Hodgdon-Beckett) circumference, the current Army 2023 one-site abdominal method (Directive 2023-11, sole-authorized 2024; the old neck+waist two-site test is deprecated), or BMI-Deurenberg — with category ranges by sex, a fat/lean mass split and FFMI scored against the ~25 natural ceiling. A fitness estimate (±3–4% vs DEXA); circumference methods approximate — use DEXA/calipers for precision.
BMI Calculator
Calculate BMI (weight ÷ height²) and classify it two ways — WHO (overweight ≥ 25, obese ≥ 30) and Asian/ICMR (overweight ≥ 23, obese ≥ 25, lower because Asian populations carry higher metabolic risk at a lower BMI). Plus your healthy weight range in kg for your height. A screening ratio that ignores muscle and fat distribution — not a diagnosis; pair it with the body-fat calculator.