· 3 min read
How to Find Your Target Weight for a Healthy BMI
The healthy BMI band of 18.5–24.9 turns into a weight range once you know your height. Here is how to work out yours step by step.
Articles by Sofia Nunes
Health & wellness writer · View profile
· 2 min read
What Would You Weigh on Other Planets?
Weight depends on gravity, but mass does not — here is why you would weigh differently on the Moon, Mars and Jupiter, and how to work it out.
· 14 min read
Blood Donation Intervals, and What Your Body Is Actually Replacing
Plasma is back in a day, red cells in weeks, iron in months — and it is the iron that sets the interval. The arithmetic of a unit, and the minimum intervals published by seven national services.
· 15 min read
Bra Sizing Is Two Measurements and Four Incompatible Systems
The band and the cup are computed differently in the UK, the US, the metric EU, the French and Spanish markets and Italy. One body, its four labels, and the arithmetic behind each.
· 14 min read
Nap Length Decides What You Get — Not How Tired You Were
A nap's effect depends on which sleep stage the alarm interrupts, and length is the only part of that you control. What 10, 20, 30 and 90 minutes actually do, with the arithmetic for the alarm.
· 11 min read
hCG Doubling Time, and What a Single Number Cannot Tell You
Doubling time is ln(2) times the interval divided by the natural log of the ratio. Here it is derived and worked on real pairs, with the two things most often got wrong online: the expected rate slows as the level rises, and a single value is meaningless because the reference range at one gestational week can span more than two hundredfold.
· 12 min read
Implantation Timing and the Window That Decides a Test Result
How early you can test is the sum of three delays: when implantation happens, how fast hCG climbs from that moment, and what the test can detect. Each one is measured in the literature, so the chain can be computed end to end — and it explains exactly why an early negative is so often wrong.
· 12 min read
Cycle Length, Ovulation, and What a Fertile Window Really Is
Ovulation is estimated far better by counting backwards from the next period than forwards from the last one, because the phase after ovulation is the stable one. Here is the inversion worked for every cycle length, the fertile window from the study that defined it, and the failure rates that make this unusable as contraception.
· 13 min read
How Pregnancy Dating Actually Works
Gestational age is counted from your last period, about two weeks before conception, so a pregnancy of 6 weeks contains an embryo of about 4 weeks. Here is Naegele's rule derived, the correction for a cycle that is not 28 days, and when ACOG says an early scan should replace your dates.
· 2 min read
How Many Calories Should You Eat Per Meal?
How to split your daily calories across meals and snacks, with typical per-meal ranges and how to adjust them to your goals.
· 3 min read
What Is a Healthy Waist-to-Height Ratio?
Keeping your waist under half your height is a simple health marker. Learn what waist-to-height ratio means, how to measure, and why under 0.5 is the goal.
· 3 min read
How Many Units Are in a Drink?
A drink's alcohol content depends on its strength (ABV) and volume. Learn how standard drinks and units are calculated and how to count yours.
· 3 min read
What Is Lean Body Mass? LBM vs Fat Mass
Lean body mass is everything in your body that isn't fat. Learn how the Boer formula estimates it and why it matters for health and training.
· 3 min read
How Much Weight Can You Safely Lose Per Week?
Health bodies suggest losing about 1-2 lb (0.5-1 kg) per week. Learn the ~500-1000 kcal/day deficit behind that and why slow-and-steady lasts.
· 3 min read
What Is Your BMR? Basal Metabolic Rate Explained
Your basal metabolic rate is the energy your body burns at complete rest. Learn how the Mifflin-St Jeor equation estimates it and what raises or lowers it.
· 14 min read
The One-Mile Walk Test, and What a VO2max Estimate Assumes
The Rockport test turns a brisk one-mile walk into a VO2max number using five inputs and one published regression. Here is the equation, one person worked through it, and the two assumptions — a stated standard error and a genuinely brisk pace — that decide whether the answer means anything.
· 12 min read
Relative Risk and Absolute Risk Are Not the Same Story
A headline saying 50% higher risk can describe a change of two-tenths of a percentage point. Both numbers come from the same 2x2 table, and computing both takes one line each — here is how, with a worked example, number needed to treat, and where the odds ratio stops approximating relative risk.
· 13 min read
Corrected Calcium: Why Albumin Changes the Number
About half of blood calcium is bound to albumin and inactive, so a total-calcium result on a low-albumin patient reads low even when the active fraction is normal. Here is the correction in both unit systems, a worked case, and the honest verdict on how badly it performs.
· 13 min read
Blood Sugar Units: mg/dL, mmol/L, and Why Both Exist
The conversion factor is not 18 — it is 18.016, and it is the molar mass of glucose divided by ten. Here is where it comes from, which countries use which unit, and every diagnostic threshold in both scales with the guideline it belongs to.
· 14 min read
Growth Percentiles: What a Child's Centile Really Means
A centile ranks a child against a reference population — it is not a grade, and one reading says almost nothing. Here is the LMS arithmetic behind the number, and why the same boy is on the 90th centile on one chart and the 85th on another.
· 12 min read
What a Standard Drink Actually Is
A standard drink is a defined mass of ethanol — and the definition changes at the border. The same glass of wine is 1.28 drinks in the United States, 1.79 in France and 2.28 in the United Kingdom.
· 12 min read
Caffeine Half-Life: Why Your Afternoon Coffee Is Still There at Midnight
Caffeine leaves by first-order kinetics, so what remains is the dose times one half to the power of elapsed time over half-life. The half-life is not a constant — it varies by multiples between people, and that is the whole story.
· 12 min read
Net Carbs: What the Subtraction Assumes
Net carbs is total carbohydrate minus fibre minus sugar alcohols. Every term in that line is a modelling choice, the first one is defined differently on each side of the Atlantic, and no regulator anywhere defines the result.
· 3 min read
How Much Water Should You Drink a Day?
How much water you really need depends on your body weight, activity and climate — not a fixed "8 glasses". Here is how to estimate your daily target.