Every formula, worked example, and free calculator for body composition, clinical scores, medication dosage, healthcare costs, and all major health calculations — verified against CDC, NIH, AAP, and peer-reviewed medical literature. 57 free calculators in one place.
Calculate BMI, TDEE, BMR, calorie burn, body fat, and weight management metrics using evidence-based formulas.
BMI (Body Mass Index) is the most widely used screening measure for weight status. It doesn't measure body fat directly but correlates well enough with body fat to be useful at the population level. The limitation: it can't distinguish muscle from fat, which is why a lean bodybuilder and an obese sedentary person of the same weight and height get the same BMI.
BMI = weight (kg) / height (m)^2
Imperial: BMI = (weight lbs x 703) / height (in)^2
Example: 170 lbs, 5'9" (69 in): BMI = (170 x 703) / (69^2) = 25.1 (overweight)
WHO categories: <18.5 underweight | 18.5-24.9 normal | 25-29.9 overweight | 30+ obese
BMR is what you burn at rest just to survive. TDEE is your actual daily burn including all activity. Every calorie-based goal — weight loss, maintenance, muscle gain — starts with knowing your TDEE. The Mifflin-St Jeor equation is the most accurate for the general population, validated in the American Journal of Clinical Nutrition (1990).
Men BMR = (10 x kg) + (6.25 x cm) - (5 x age) + 5
Women BMR = (10 x kg) + (6.25 x cm) - (5 x age) - 161
TDEE = BMR x Activity factor (1.2 sedentary → 1.9 extra active)
Example (male, 80kg, 180cm, 30yr, moderate): BMR = 1,780 | TDEE = 2,759 kcal
MET (Metabolic Equivalent of Task) values represent how many times more energy an activity requires compared to sitting still. Walking at a moderate pace is 3.5 METs; running at 6 mph is 9.8 METs. Multiply by weight in kg and time in hours to get calories burned.
Calories burned = MET x Weight (kg) x Duration (hours)
Example: 70kg person running 30 min at 6 mph (MET 9.8): 9.8 x 70 x 0.5 = 343 kcal
Walking (3.5 METs), cycling moderate (8.0), swimming laps (7.0), weight lifting (5.0)
The simple rule is 35 mL per kg of body weight per day, which lands most adults between 2 and 3 liters. Exercise and heat add to this baseline. The Institute of Medicine recommends 3.7 L total daily water for men and 2.7 L for women from all sources (including food, which contributes about 20%).
Weight loss % = ((Start weight - Current weight) / Start weight) x 100
Example: 220 lbs → 195 lbs: ((220-195)/220) x 100 = 11.4% lost
Clinical significance: 5% weight loss reduces cardiovascular and metabolic risk meaningfully
Validated clinical calculators for INR, cardiac output, ABI, PVR, PSA density, and other hemodynamic and laboratory values.
INR (International Normalized Ratio) standardizes prothrombin time (PT) testing across different laboratories and reagents. Without standardization, a PT of 20 seconds at one lab might represent different clotting risk than 20 seconds at another lab. INR eliminates that variability. For warfarin patients, the therapeutic window of 2.0–3.0 must be maintained carefully: too low means clot risk, too high means bleeding risk.
INR = (Patient PT / Mean Normal PT) ^ ISI
Normal INR: 0.8 to 1.2 | Warfarin target: 2.0 to 3.0 | Mechanical valve: 2.5 to 3.5
PT = prothrombin time (seconds) | ISI = International Sensitivity Index of reagent
Cardiac Output (CO) = Heart Rate (bpm) x Stroke Volume (mL/beat) / 1000
Normal CO: 4.0 to 8.0 L/min | Cardiac Index = CO / BSA (normal 2.5 to 4.0 L/min/m²)
Example: HR 72 bpm x SV 70 mL = 5,040 mL/min = 5.04 L/min
PVR (dynes·sec·cm⁻⁵) = 80 x (mPAP - PAWP) / Cardiac Output
Normal PVR: 37-250 dynes·sec·cm⁻⁵ | Wood units = (mPAP - PAWP) / CO
PVR above 250 dynes or 3 Wood units indicates pulmonary vascular disease
PSA Density = PSA (ng/mL) / Prostate Volume (mL)
PSA density > 0.15 ng/mL/mL: Higher risk of clinically significant cancer
Example: PSA 8 ng/mL, prostate 40 mL: density = 8/40 = 0.20 (elevated)
ABI = Ankle systolic pressure / Arm (brachial) systolic pressure
Normal: 1.0 to 1.4 | Mild PAD: 0.7-0.9 | Moderate PAD: 0.4-0.7 | Severe: <0.4
| Test | Normal Range | Clinical Use |
|---|---|---|
| INR | 0.8 – 1.2 | Warfarin management, clotting disorders |
| Cardiac Output | 4.0 – 8.0 L/min | Heart failure, ICU hemodynamics |
| Cardiac Index | 2.5 – 4.0 L/min/m² | Normalized for body size |
| PVR | 37 – 250 dynes·sec·cm⁻⁵ | Pulmonary hypertension, transplant evaluation |
| ABI | 1.0 – 1.4 | Peripheral artery disease screening |
| PSA Density | <0.15 ng/mL/mL | Prostate cancer vs. BPH differentiation |
| D-dimer (age-adjusted) | Age x 10 μg/L (age >50) | PE/DVT rule-out in older patients |
| AST/ALT ratio | <1.0 | >2.0 suggests alcoholic liver disease |
Weight-based pediatric dosing, mg-to-mL conversions, dosage unit conversions, and medication detection windows.
Weight-based dosing is the standard for pediatric medications because children can't simply receive smaller versions of adult doses — their pharmacokinetics differ significantly. The formula is straightforward, but the concentration of the liquid formulation adds a second step that trips up many parents.
Dose (mg) = Prescribed dose (mg/kg) x Patient weight (kg)
Volume (mL) = Dose (mg) / Concentration (mg/mL)
Infant Tylenol example: 12.5 mg/kg for 10 kg child = 125 mg
At 160 mg/5 mL (= 32 mg/mL): 125 / 32 = 3.9 mL
mg to mcg: multiply by 1,000 | mcg to mg: divide by 1,000
mg to mEq: mEq = (mg / molecular weight) x valence
Units to mg: varies by drug (insulin: 1 unit ≠ fixed mg)
IU to mg: drug-specific conversion (e.g., Vitamin D: 40 IU = 1 mcg)
ETG (ethyl glucuronide) is a direct urine biomarker of alcohol consumption, detectable far longer than alcohol itself. The detection window depends on the amount consumed. ETG is used in zero-tolerance monitoring programs, court-ordered testing, and workplace programs. The standard threshold is 100–500 ng/mL depending on the laboratory.
Days supply = Total pills / Prescribed pills per day
Refill date = Fill date + Days supply - Buffer days (typically 5-7)
Example: 90 pills, 3 per day = 30-day supply | Refill window opens at day 23-25
| Medication | Typical Dose Range | Formulation Note |
|---|---|---|
| Infant acetaminophen | 10–15 mg/kg/dose | 160 mg/5 mL standard since 2011 |
| Ibuprofen (children) | 5–10 mg/kg/dose | Not for infants under 6 months |
| Tesamorelin | 2 mg subcutaneously daily | HIV-associated lipodystrophy only |
| ETG urine window | 1–5 days | Threshold: 100–500 ng/mL |
| Plan B (levonorgestrel) | 1.5 mg single dose | Within 72 hrs; efficacy decreases over time |
Estimate the true cost of dental work, surgeries, hearing aids, mental health therapy, senior care, and drug rehabilitation.
Healthcare is one of the largest and most unpredictable household expenses. Unlike most consumer purchases, the price is rarely disclosed upfront — which means patients often face bills far larger than expected. These calculators give you a reasonable cost range before you commit, so you can budget, compare providers, and understand what insurance should cover.
| Procedure / Service | Average Cost (US 2026) | Insurance Typically Covers |
|---|---|---|
| Dental implant (single) | $3,000 – $5,500 | 10–50% (varies) |
| Dental crown | $800 – $2,500 | 50% after deductible |
| Invisalign full treatment | $3,000 – $9,000 | Ortho coverage max (often $1,500) |
| Hip replacement | $30,000 – $60,000 | 80–90% after deductible |
| Bariatric surgery | $15,000 – $30,000 | Varies; BMI >40 or >35 + comorbidity |
| Hearing aid (pair) | $2,000 – $7,000 | Rarely covered by standard insurance |
| Therapy (per session) | $100 – $300 | $20–60 copay (if in-network) |
| Drug rehabilitation (30-day) | $6,000 – $60,000 | ACA-required mental health benefit |
| Nursing home (annual) | $85,000 – $120,000 | Medicare: limited; Medicaid: after spend-down |
| Senior living comparison | $3,500 – $8,500/mo | Self-pay; some long-term care insurance |
If you don't enroll in Medicare Part B during your Initial Enrollment Period and don't have qualifying coverage, you'll pay a permanent premium penalty. The penalty is 10% of the standard Part B premium for each full 12-month period you delayed enrollment. At a $174.70/month standard premium (2024), even a 2-year delay adds $34.94/month — permanently, for life.
Medicaid's asset limit for long-term care is approximately $2,000 in most states for an individual. If you have more than this, you must "spend down" excess assets before Medicaid covers nursing home costs. Planning ahead with an elder law attorney can protect spousal assets within the Community Spouse Resource Allowance (CSRA) of $30,828–$154,140 depending on state.
Eye prescription conversion, children's growth percentiles, pregnancy due date, and pet health calculations.
An eye prescription contains sphere (SPH), cylinder (CYL), and axis values. Sphere indicates the main refractive power in diopters — negative for myopia (nearsighted), positive for hyperopia (farsighted). Cylinder and axis describe astigmatism. The contact lens vertex conversion is needed because contacts sit directly on the eye while glasses are 12–14 mm away — the effective power differs at high prescriptions.
Vertex-adjusted power = 1 / (1 / Spectacle power - Vertex distance in meters)
Vertex distance: typically 0.012 to 0.014 meters (12-14 mm)
Significant above +/-4.00 diopters; smaller prescriptions need no adjustment
The CDC growth charts (revised 2000, updated 2022) define height and weight percentiles for children aged 2–20 using data from nationally representative samples. A child at the 50th percentile is at the median for their age and sex. Below the 5th or above the 95th percentile warrants pediatric evaluation. Percentile position is more important than any single measurement — consistent tracking over time matters most.
Due date = First day of last menstrual period + 280 days (40 weeks)
Or: LMP + 9 calendar months + 7 days
Assumes regular 28-day cycle; adjusts for cycle length variations
The old "1 year = 7 dog years" rule is an oversimplification. Research published in Cell Systems (2020) shows dogs age rapidly in their first two years, then more slowly. A 1-year-old dog is equivalent to about 30 human years; a 4-year-old dog is roughly 52 human years. Small breeds age slightly more slowly than large breeds after age 2.
Calculate chemical doses for pool chlorination, salt levels for saltwater pools, and pH balancing.
A safe, clear pool requires maintaining six parameters simultaneously. pH is the most critical: if pH is wrong, every other chemical is less effective. Free chlorine (FC) sanitizes; combined chlorine (CC) indicates chloramine buildup from bather waste. Alkalinity buffers pH from swinging too fast. Cyanuric acid (CYA) protects chlorine from UV degradation.
| Parameter | Target Range | If Outside Range |
|---|---|---|
| pH | 7.2 – 7.6 | pH down (muriatic acid) or pH up (soda ash) |
| Free Chlorine (FC) | 2 – 4 ppm | Add liquid chlorine or shock treatment |
| Total Alkalinity (TA) | 80 – 120 ppm | Sodium bicarbonate to raise; muriatic acid to lower |
| Cyanuric Acid (CYA) | 30 – 50 ppm | Add stabilizer to raise; dilute to lower |
| Calcium Hardness | 200 – 400 ppm | Calcium chloride to raise; dilution to lower |
| Salt (saltwater pool) | 2,700 – 3,400 ppm | Add pool salt (NaCl) to raise; dilute to lower |
ppm increase needed = Target FC - Current FC
Liquid chlorine (10% NaOCl): oz needed = Pool gallons x ppm increase / 75,000
Example: 20,000-gallon pool, raise FC from 1 to 4 ppm (3 ppm increase):
oz = 20,000 x 3 / 75,000 = 0.8 oz... use label formula for exact product strength
Salt needed (lbs) = Pool volume (gallons) x (Target ppm - Current ppm) / 1,000,000 x 8.34
Example: 15,000-gallon pool, current 0 ppm, target 3,200 ppm:
Salt = 15,000 x 3,200 / 1,000,000 x 8.34 = 400 lbs of pool salt
All formulas and reference data on this guide are sourced from authoritative medical, government, and clinical standards: