Women's Health calculators
Cycle, conception and pregnancy timelines based on standard obstetric dating.
1 calculator in this section
What the dating assumes
Pregnancy is dated from the first day of the last menstrual period rather than from conception, because that is the date most people can actually recall. It also means gestational age runs about two weeks ahead of the embryo's true age. Naegele's rule then adds 280 days and assumes a 28-day cycle with ovulation on day 14, which describes a minority of cycles: for a consistent 35-day cycle the unadjusted date can be a week early. Only about 4% of births happen on the estimated date, and a first-trimester crown-rump length measurement beats any calculation, which is why clinicians revise the date after the dating scan.
Women's Health guides
Returning to Exercise After Birth: A Staged, Evidence-Led Approach
The six-week check is a clearance, not a starting line. Here is what the guidelines say about postpartum activity, how return is usually staged, and who to ask.
Nutrition During Pregnancy: What Changes, and by How Much
Pregnancy raises requirements for several nutrients far more than it raises energy needs. Here is what the evidence supports, what it does not, and where the numbers come from.
The Menstrual Cycle and Training: What the Evidence Does and Doesn't Support
Cycle-based training programmes promise more than the research delivers. Here is what the literature actually shows, why its quality is poor, and what is worth acting on.
Pregnancy Weight Gain: What the Guidelines Actually Say
The IOM ranges are set by pre-pregnancy BMI, not by weight during pregnancy. Here is where those numbers came from, what they do and do not predict, and why your target belongs to your care team.
Gestational Age Explained: Why Pregnancy Is Dated From Before Conception
Pregnancy is counted from the last menstrual period, a fortnight before conception. Here is why that convention exists, what Naegele's rule assumes, and why dating is a window.