Measure consistently
Track the first day of bleeding across several cycles and use the observed spread rather than relying on one textbook cycle length.
Menstrual-cycle projection
Plan the next six periods with a visible variability range.
Project period start and end dates, early/late ranges and cycle-day ovulation midpoints from an average cycle without hiding normal calendar uncertainty.
The calculation runs locally in this browser. Educational outputs do not replace professional assessment, diagnosis, treatment or emergency care.
Method and interpretation guide
Use the period projection result as a transparent estimate
Track the first day of bleeding across several cycles and use the observed spread rather than relying on one textbook cycle length. The worksheet exposes its assumptions so the result can be checked instead of accepted as a black box.
Read the assumptions
Cycle length naturally varies and an average cannot guarantee a date. Hormonal contraception, postpartum changes, illness, stress and life stage can change the pattern.
Escalate important decisions
A calculator cannot examine symptoms, medical history, medication effects or measurement quality. Use qualified professional guidance when the decision has health consequences.
Local calculation
Inputs are processed in this browser. No account or external calculator is required to produce the result.
False precision
Extra decimal places do not remove biological variation, input error or limits in the underlying population equation.
Scope
Cycle length naturally varies and an average cannot guarantee a date. Hormonal contraception, postpartum changes, illness, stress and life stage can change the pattern.
Simple by design
Three steps to a clearer number.
Enter your details
Use realistic values in each field. You can change them anytime.
Calculate instantly
The formula runs locally, so there is no account or waiting time.
Use the result
Treat the answer as a practical estimate for your next decision.