· 4 min read
How to Estimate Your Conception Date
Estimate conception from your last period or your due date, understand ovulation timing, and know why the result is a range rather than a single day.
Articles by Sofia Nunes
Health & wellness writer · View profile
· 3 min read
How Much Caffeine Is Safe Per Day?
The 400 mg daily guideline for adults, how much caffeine is in coffee, tea, cola and energy drinks, and why sensitivity varies from person to person.
· 3 min read
How Much Fiber Per Day Do You Need?
Daily fiber targets of 25 to 38 grams by sex and age, why fiber matters for digestion and heart health, and the best food sources to hit your goal.
· 3 min read
How Much Sodium Per Day Is Safe?
The 2,300 mg FDA limit, the 1,500 mg ideal from the AHA, and why most sodium is hidden in packaged food — plus how to read labels and cut back.
· 3 min read
How Much Sugar Per Day Is Healthy?
The WHO limit on free sugars, how to turn a percentage of calories into grams, and where hidden sugar comes from — with practical daily targets.
· 3 min read
How to Convert Steps to Distance
To turn a step count into distance, multiply your steps by your stride length. Learn how to estimate your stride and convert steps into miles.
· 3 min read
Best Time to Wake Up: Using Sleep Cycles
Sleep runs in cycles of about 90 minutes. Waking at the end of a cycle can help you feel more refreshed. Here's how to count back from your wake time.
· 12 min read
IVF Dating Is the One Case Where the Date Is Actually Known
Every other pregnancy is dated from an estimate. After IVF, fertilisation is timed to the hour, so gestational age is arithmetic: 266 days from fertilisation, minus the embryo's age at transfer. Here is the derivation for day-3, day-5 and day-6 embryos, why frozen and fresh transfers use the same rule, why an early scan rarely moves an IVF date, and what the two-week offset on a scan report means.
· 13 min read
Am I Overweight? Why One Number Cannot Say
BMI reads muscular bodies as heavy and cannot see where fat sits at all — which is exactly why the waist measures exist. Here are the published waist and waist-to-height thresholds, a worked case where BMI and waist give opposite answers, an honest account of the contested mortality curves, and the 2025 shift toward defining obesity by adiposity and organ function rather than by a ratio.
· 11 min read
Am I Underweight? What the Question Is Really Asking
The 18.5 cut-off is a population screening line, not a diagnosis. Here is where it comes from, what the mortality data below it actually show, and the three things it cannot see: body composition, recent change — which is far more informative than the level — and the fact that the same line does not fit every age or every population.
· 3 min read
Blood Pressure Ranges Explained
Blood pressure has two numbers: systolic and diastolic, measured in mmHg. Learn the ACC/AHA categories from normal to hypertensive crisis and what they mean.
· 12 min read
What Breastfeeding Actually Costs in Energy — and Why the Published Number Is Smaller Than the Milk
Milk production has a computable cost: volume times energy density divided by the efficiency of conversion. Do the sum and you get about 675 kcal a day, not the 500 that gets quoted. Here is the derivation, why the published increment is deliberately lower, how much the real spread is between mothers, what the water requirement actually rests on, and why cutting calories while feeding is a clinical question.
· 13 min read
Eating for Two Is About Three Hundred Calories — and Almost None of Them in the First Trimester
The extra energy a pregnancy costs is far smaller than the phrase suggests, and it arrives on a schedule: near zero in the first trimester, modest in the second, real in the third. Here are the published increments from EFSA, FAO/WHO/UNU and the 2023 US reference intakes, what they look like as food, and why protein and folate rise proportionally faster than calories do.
· 3 min read
Resting Heart Rate by Age: What's Normal?
A normal resting heart rate for adults is usually 60 to 100 beats per minute. Learn what affects it, why athletes run lower, and when a reading may be concerning.
· 13 min read
How Many Calories Does a Run Actually Burn?
Running costs roughly 0.73 kcal per pound per mile — one kilocalorie per kilogram per kilometre in the units the physiology is published in — and, this is the counterintuitive part, the figure barely moves with pace. Here is the derivation from the ACSM equation, the corrections that matter, and why grade changes it far more than speed.
· 3 min read
What Is Blood Alcohol Content (BAC)?
Blood alcohol content measures the concentration of alcohol in your blood. Learn how BAC is estimated with the Widmark formula and why legal limits differ by country.
· 12 min read
The Calories in a Drink Are Mostly the Alcohol
Ethanol carries 7 kcal per gram and the arithmetic is exact: volume × ABV × 0.789 × 7. A dry spirit is almost pure alcohol calories; a liqueur is nearly half sugar. Here is the derivation, the table, and the metabolic caveat stated without overclaiming.
· 13 min read
What a Meal Plan Generator Can and Cannot Know
A generator solves a constrained arithmetic problem — hit an energy target, hit the macro splits, stay inside a food list — and it does that well. Here is the arithmetic that makes a plan work, and the honest list of what no generator can see.
· 14 min read
How Much Carbohydrate Do You Actually Need?
There is a small hard answer — the brain's glucose demand, published as 130 g a day — and a very large soft one. Above the minimum, carbohydrate need scales with training volume in grams per kilogram, not with a percentage.
· 16 min read
How Long Until You Are Sober? Zero-Order Elimination Explained
Alcohol leaves the body at a roughly constant mass per hour, whatever the concentration. That one property — zero-order elimination, unlike caffeine's exponential decay — explains why doubling the dose doubles the time, why nothing speeds it up, and why every estimate carries a wide error bar. With the Widmark relation worked through, and each market's legal limit stated separately.
· 13 min read
Caffeine Against Sleep Pressure: What It Blocks, and What It Cannot
Sleep is regulated by two processes: a pressure that builds with every waking hour, and a clock. Caffeine acts on neither directly — it blocks the receptors that report the pressure. The pressure keeps building behind the block, which is why the crash arrives and why an afternoon dose costs that night's sleep even when you do not feel it.
· 14 min read
Baby Growth, and What Crossing Centiles Actually Means
The WHO infant standard is prescriptive: it was built from healthy breastfed babies and describes how infants should grow. National references describe how they did grow. In the first year the two disagree by enough to move the same baby forty percentile points, with no change in the baby. Here is the size of the gap, and what the published thresholds for concern actually say.
· 12 min read
Where a Percentile Comes From: Which Population, Measured When
A percentile is a rank against a reference population, so the first question is never the arithmetic — it is which population, measured when. The same 5'11" man is the 38th percentile in one national dataset and the 86th in another, and the 91st against a reference of people born a century ago. Here is why, and what a z-score adds.
· 14 min read
How Tall Will a Child Be? The Arithmetic Is Easy; the Error Bar Is the Story
Average the parents' heights, shift by a sex constant, and you have a target height. The honest part is what comes next: the published prediction interval is about ±4 inches, wide enough to cover most of the adult population. Here is the formula, the interval, why bone age does better, and why children keep out-growing the target.