What actually happens
in a cycle.
Straight answers about what a cycle is, what can be predicted, what cannot, what the four phases actually are, when a symptom is worth a doctor's time, and where the popular stories about the body came from.
Everything under this
When Will I Get My Period? What a Quiz Can and Can't Tell You
Every quiz that promises a date is guessing. Here is what the signs actually mean, what the timelines usually look like, and an estimator that gives you a range and admits it.
Read it 7 min read · 6 sourcesThe Moon and Your Menstrual Cycle: What the Research Actually Found
Two rhythms of about twenty-nine days, and a very old story about why. Here is what the studies actually found — including the ones that found nothing.
Read it 7 min read · 8 sourcesThe Menstrual Phase, Explained: What Is Actually Happening While You Bleed
Day one is the first day of full flow, and every number on this site is built on that one date. What the bleeding days are, what commonly comes with them, and where the ordinary ends.
Read it 7 min read · 7 sourcesThe Follicular Phase: The Half of Your Cycle That Does the Moving
The first half of the cycle is the part that stretches. What happens in it, why a long cycle is usually a long first half, and what that does to every date a calculator prints.
Read it 7 min read · 10 sourcesOvulation Explained: The Signs, the Timing, and What the Evidence Shows
Ovulation is a distribution, not a date. What each sign can genuinely see, how far ahead it sees it, and how strong the evidence under it is.
Read it 7 min read · 6 sourcesThe Luteal Phase: How Long It Really Lasts, and What Moves It
The textbook says fourteen days. The measurement says 12.4, with 18% of cycles under 11. What happens in the second half of a cycle, and how to work out your own.
Read it 6 min read · 7 sourcesCycle Length: What Is Normal, and What the Numbers Actually Say
Four respectable bodies, four different answers, all on one chart. Then the numbers from 612,613 real cycles, and what to do with your own.
Read it 7 min read · 8 sourcesIrregular Periods: When Normal Variation Is Worth a Conversation
Almost everybody thinks their periods are irregular, and most are describing ordinary movement. Here is what the word means to the NHS, to ACOG and to NICHD, and where each of them draws the line.
Read it 6 min read · 8 sourcesWhy Is My Period Late? The Ordinary Explanations, and the Ones to Check
A late period is nearly always a late ovulation, which is why the delay sits in the first half of the cycle. The ordinary explanations, in prose, for somebody who wants to understand rather than count.
Read it 8 min read · 9 sourcesPeriods After Stopping the Pill: What Comes Back, and When
What comes back is ovulation, and the period follows it. Here is what the NHS says by method, what one matched study measured, and the number nobody can honestly give you.
Read it 6 min read · 6 sourcesStress and Your Cycle: What Stress Can Actually Do to a Period
Stress is the explanation everybody reaches for, and it is both real and over-used. It moves the timing of a cycle; the studies that show that also show what it does not move.
Read it 7 min read · 6 sourcesPeriod Pain: What Is Normal, What Is Not, and When to Ask Someone
More than half of women who menstruate have some pain for a day or two each month. Here is the shape ordinary pain takes, the shape worth an appointment, and the thresholds the NHS puts between them.
Read it 8 min read · 6 sourcesPMS: What the Evidence Says About the Symptoms, the Timing and the Relief
PMS is defined by when symptoms arrive, not by which ones. Here are ACOG's criteria, the overlap nobody prints, and why two cycles of dated entries beat any symptom list.
Read it 8 min read · 6 sourcesPMDD: An Honest Overview of Premenstrual Dysphoric Disorder
A recognised condition, the diagnostic criteria a clinician actually applies, prevalence figures that disagree with each other, and the NHS's emergency advice printed high rather than buried.
Read it 7 min read · 7 sourcesHeavy Periods, Honestly: What Counts as Heavy and What to Do About It
Nobody can see anybody else's period, so heavy usually gets judged against friends who are also guessing. The NHS answers it with seven concrete tests, and this page prints all seven.
Read it 6 min read · 6 sourcesSpotting Between Periods: The Honest List of What Causes It
Blood you were not expecting has a long list of causes, ordinary and serious, and the bleeding itself does not tell them apart. The urgent exception first, then the honest list.
Read it 7 min read · 6 sourcesYour Cycle and Sleep: What Changes, What Does Not, and What Helps
Reported sleep gets worse before a period; measured sleep barely moves. What that gap means, what does change in the laboratory, and why none of it says the tiredness is imaginary.
Read it 8 min read · 6 sourcesYour Cycle and Exercise: What the Evidence Supports, and What It Does Not
A meta-analysis of 78 studies found a trivial effect and refused to write guidelines. An umbrella review found no strength difference in 9 of 10 quality studies. Here is what that leaves you with.
Read it 8 min read · 6 sourcesBBT Charting: How to Take a Basal Body Temperature and Read the Chart
The method done properly, and its ceiling in the same breath. A temperature chart records what has already happened — and against hormone-confirmed ovulation across 193 cycles, the shift showed up in under a quarter of them.
Read it 7 min read · 6 sourcesCervical Mucus Tracking, Honestly: What It Shows and What It Cannot
The one sign that looks forwards, with both of its numbers. Beginners identified a peak day in 63% of cycles; the figure everybody quotes comes from women who had been taught. That gap is the article.
Read it 6 min read · 9 sourcesThe First Ovulation After Periods Start: What the Early Years Look Like
A period is not proof that an ovulation happened. Half of all cycles in the first two years are anovulatory even when they arrive on time — what the early years look like, and the two numbers worth carrying.
Read it 6 min read · 12 sourcesPeriod Myths, Debunked: Fifteen Things That Are Not True
Fifteen things repeated everywhere that the evidence does not support — the 28-day cycle, day-14 ovulation, the fixed second half, the Moon — each with the correction and the study it came from.
Read itHow to read these. Every page under this heading links the source of each claim, and every statement about a named app is quoted from that company's own published policy or support page rather than from a review, a memory or a marketing site. Where something cannot be checked, the page says so instead of guessing.
Nothing here is medical advice, none of it is legal advice, and none of it replaces someone who knows your history.
The tools these pages point at
Period Calculator
Your last period plus your usual cycle length, and the next few months laid out on the moon ring — with the spread you should actually expect.
Open itPrintable Period Tracker
Build a paper tracker for any month or a whole year, then print it. Flow key, symptoms, an optional temperature row — and a gentler version for a first tracker.
Open itCycle Length Calculator
Log a few period start dates and read your own numbers: average, shortest, longest, and how much the whole thing moves.
Open itCycle Phase Calculator
Which phase you are probably in today, what is actually happening in it, and a straight answer about how blurred the edges between them are.
Open itOvulation Calculator
The days ovulation is most likely, worked backwards from your next period — printed as a window, because a single day would be invented.
Open itOvulation Test Calculator
Which day to start an ovulation test, how many days to keep going, and a straight answer about what a positive one does and does not mean.
Open itPrintable BBT Chart
Graph paper for a cycle: a temperature grid in °C or °F, a row for the coverline, and space for the notes that make a chart readable later.
Open itLuteal Phase Calculator
The days from ovulation to your next period — counted exactly when you know the date, and estimated with the uncertainty shown when you do not.
Open itPeriod Late Calculator
How late is late, measured against your cycle rather than a textbook one — plus the ordinary explanations, and the day a test would actually mean something.
Open itPregnancy Test Calculator
Three ways in — ovulation, conception, or your last period — and two dates out: the earliest a test is worth taking, and the day its answer can be trusted.
Open itPrintable Period Symptom Tracker
A month across the top, your symptoms down the side, one box a day. Rename every row, print one page, and bring the pattern to the appointment.
Open itFirst Period Kit Checklist
What to put in a school bag and what to keep at home, on one printable page. Editable, unfussy, and written to be reassuring rather than dramatic.
Open itAthena keeps all of this on your phone.
The calculators here forget you the moment you close the tab. Athena is the same arithmetic living on your device — the moon ring, an honest calendar with ranges instead of false precision, and a database that never leaves the phone because there is no account and no server behind it.
In development for iPhone and Android. Not released yet — when it is, it will be on this site.
What Athena is