Health & Fitness Numbers
What the calculators actually compute, where the formulas came from, and how much they can honestly tell you.
Add 280 days to the first day of the last period and you have the standard estimate — here's the arithmetic, a worked example, and why only about 1 in 20 babies actually arrive on that exact day.
Wider spacing, one sentence per line, cautious syllable marks — a look at what a decoding-focused reformat actually does to a page of text, and what it deliberately leaves alone.
"After I brush my teeth, I'll stretch, read and journal" only works if the minutes actually fit — here's the arithmetic for splitting a time budget evenly, remainder and all.
Gym three times, study twice, laundry once a week — working out which days get what, and which day ends up with nothing, is arithmetic you can do with a week's grid and a pencil.
The shelf life of expressed milk depends on where it's stored and when the clock actually started — which isn't always when you pumped. Here are the CDC limits, worked through by hand.
The body that sets US nutrition guidelines publishes an Adequate Intake by life stage — and explicitly refuses to give a per-person ounce formula. Here's the official number, split out by hand, next to the popular rule it doesn't endorse.
Ovulation tracking apps all run the same back-of-the-envelope rule: count back 14 days from your next expected period. Here's the arithmetic, with a worked example.
The Widmark-style formula behind most free BAC calculators is just three numbers and a subtraction. Worth understanding exactly because it is far too crude to make a driving decision on.
Bunching four workouts into Monday-to-Thursday leaves three rest days stacked at the end. One simple rule spaces any number of days across a week as evenly as seven days allow.
"Drink eight glasses a day" ignores that a 60 kg adult and a 100 kg adult don't need the same amount. A single per-kilogram multiplier gets you a number scaled to you.
Waking mid-cycle is what makes mornings feel rough, not the total hours slept. Count backward in 90-minute blocks from your alarm and you can pick a bedtime that lands you at the end of one instead.
BMR is what your body burns lying still; TDEE scales that up for the life you actually live — and the whole calculation is five multiplications you can do on paper.