Menstria · interactive
Your whole cycle, on one wheel.
A cycle is hard to picture as a list of dates. As a circle it becomes obvious: the bleeding at the top, ovulation roughly two weeks before the next period, and the fertile window sitting just before it — not after.
Drag the wheel to any day. Nothing you enter leaves your browser.
The first day of actual bleeding, not spotting.
One thing worth knowing before you start. This wheel estimates ovulation by counting back 14 days from your next expected period, because the luteal phase is the reliably fixed half of the cycle. That estimate is only as good as the assumption that your cycles are regular.
It is a map, not a test. It does not detect ovulation, and it should not be used as contraception.
Your cycle
Day 1
How the fertile window actually works
The fertile window is six days long and it ends on the day of ovulation. That surprises people, because the intuition is that the egg has to come first. In fact sperm survive in the reproductive tract for several days while the egg survives roughly 12 to 24 hours — so the days before ovulation carry nearly all of the chance.
| Day relative to ovulation | Probability of conception from intercourse on that day alone |
|---|---|
| 5 days before | 0.10 |
| Day of ovulation | 0.33 |
| After ovulation | Essentially none in that cycle |
Wilcox AJ, Weinberg CR, Baird DD. N Engl J Med. 1995;333(23):1517–21. 221 women planning pregnancy, ovulation estimated from daily urinary estrogen and progesterone metabolites. Conception occurred only when intercourse fell within the six-day window ending on the estimated day of ovulation.
Why this wheel does not offer to help you conceive a boy or a girl. The best-known method for this — timing intercourse relative to ovulation, popularised in the 1980s — was tested in the same study that established the fertile window. Cycles producing male and female babies had indistinguishable patterns of intercourse relative to ovulation. Earlier analyses of natural family planning cohorts had already contradicted the theory.
Giving timing instructions for sex selection would mean giving instructions that do not work, to people making decisions that matter to them. So this tool does not, and says why instead.
Evidence base
Sources
Vancouver format, numbered in order of first use.
- Wilcox AJ, Weinberg CR, Baird DD. Timing of sexual intercourse in relation to ovulation. Effects on the probability of conception, survival of the pregnancy, and sex of the baby. N Engl J Med. 1995;333(23):1517–1521. doi:10.1056/NEJM199512073332301 221 healthy women planning pregnancy, with ovulation estimated from daily urinary estrogen and progesterone metabolites. Source of the six-day fertile window ending on the day of ovulation, and of the conception probabilities used here — 0.10 five days before ovulation rising to 0.33 on the day itself. Also the source for the statement that cycles producing male and female babies showed similar patterns of intercourse relative to ovulation.
- Gray RH. Natural family planning and sex selection: fact or fiction? Am J Obstet Gynecol. 1991;165(6 Pt 2):1982–1984. Analysis across natural family planning cohorts contradicting the proposition that the sex of offspring can be selected by timing intercourse around ovulation. Cited alongside Wilcox because the two are independent and reach the same conclusion.
- Munro MG, Critchley HOD, Fraser IS; FIGO Menstrual Disorders Committee. The two FIGO systems for normal and abnormal uterine bleeding symptoms and classification of causes of abnormal uterine bleeding in the reproductive years: 2018 revisions. Int J Gynaecol Obstet. 2018;143(3):393–408. doi:10.1002/ijgo.12666 Source of the normal ranges the wheel checks your entries against: cycle frequency 24 to 38 days, bleeding duration 8 days or fewer.
- Bull JR, Rowland SP, Berglund Scherwitzl E, et al. Real-world menstrual cycle characteristics of more than 600,000 menstrual cycles. NPJ Digit Med. 2019;2:83. Population mean cycle length of approximately 29.3 days with wide spread, and the basis for treating 28 days as a convention rather than a norm.
On the embryo development timeline. Days shown after ovulation assume fertilization occurred on the day of ovulation and describe typical timing. Implantation normally occurs 6 to 12 days after ovulation, and there is real biological variation around every stage. These are illustrative, not a schedule your body is obliged to follow.
On moon phases. Included because people enjoy seeing them and some track by them. There is no established relationship between lunar phase and the timing of menstruation or ovulation, and none is implied here.