Guides
Clear explanations of the cycle math, body signs, and dating conventions behind the calculators — including what each estimate can and cannot tell you.
Start with a question
Each guide links to the matching calculator and related tools.
How to Calculate Your Next Period
Use your last period date and average cycle length to estimate the next one, and learn why the date can shift.
Read guideOvulation Signs and Your Fertile Window
What calendar estimates, cervical mucus, basal body temperature, and ovulation tests can — and cannot — tell you.
Read guideHow Pregnancy Due Dates Are Calculated
The 280-day rule, cycle-length adjustment, ultrasound dating, and why most babies are not born on the exact date.
Read guideWhen to Call Your Care Team About Contractions
How to time contractions, what the pattern can tell you, and the warning signs that need urgent help.
Read guideHow to use these guides
Start with the question closest to your situation, then use the linked calculator. The guides explain the assumptions behind each result so you can judge whether an estimate is useful for you. They are general education, not a diagnosis or a plan for medical care.
If you are trying to conceive, want to avoid pregnancy, or have concerns about your cycle or pregnancy, talk with a qualified healthcare professional. A calculator cannot assess your individual health or replace an appointment.
General references
These organizations provide general health information. They are external sites with their own content and policies, and this site is not affiliated with them.