About HealthFit

HealthFit is a cluster of small calculators for everyday health and fitness questions: body composition, energy balance, pregnancy and ovulation timing, training intensity, and hydration. The site is written for people who already know what they are estimating — a runner checking a heart-rate zone before intervals, a new parent figuring out a due-date window, a college student looking up their basal metabolic rate to size a meal plan — and want the number first, with the underlying formula visible in case it matters.

The audience is broad, but the editorial line is narrow: HealthFit publishes estimates, not diagnoses. The BMI calculator returns a category. The TDEE calculator returns a calorie window. The due-date and ovulation tools return calendar dates with a confidence range. These numbers are a starting point for a conversation with a clinician, coach, or registered dietitian — never a replacement for one.

Where the formulas come from

BMR on HealthFit uses the Mifflin-St Jeor equation (1990), which is the formula recommended by the American Dietetic Association as the most accurate predictive equation for healthy adults. TDEE multiplies BMR by an activity factor from the standard Harris-Benedict activity scale. Heart-rate zones default to the Karvonen method (heart-rate reserve) and offer the Tanaka revision (208 - 0.7 × age) as a maximum-HR alternative. The pregnancy due-date tool uses Naegele’s rule (LMP + 280 days) and exposes the conception-date and ultrasound-based alternatives. The ovulation calculator computes the fertile window around the predicted ovulation day. Each tool’s formula and assumptions are documented on its own page.

Editorial cadence

Health guidelines change. The default ranges on calculators tied to clinical thresholds — BMI categories, blood pressure brackets, pediatric growth references — are re-checked against the relevant authority (CDC, WHO, ACOG, ACSM) on a quarterly cadence. When a guideline moves, the page is updated and the source is cited inline. HealthFit is published by the inovisum team; we are not a medical practice, do not provide care, and are not a substitute for the clinicians who do.