Period Calculator
Estimate upcoming period dates from your most recent period and usual cycle pattern.
Your details
Enter only the information needed for this estimate.
Complete the fields and select “Estimate my next periods” to see your estimate.
Your next estimated periods
These projected dates can help with planning, supplies, travel, and symptom tracking.
A period arriving earlier or later than this estimate does not by itself explain why the cycle changed.
Make it useful beyond today
Support your cycle beyond one estimate
Build small daily routines for steadier energy, sleep, and stress support.
How dates are projected
The calculator adds your average cycle length to the first day of your latest period. It repeats that interval to show future estimates and uses your usual bleeding length to shade likely period days.
The projection becomes less certain farther into the future because each estimate assumes the same cycle length.
When tracking is useful
A simple period log can reveal whether a timing change is occasional or becoming a pattern. Dates are helpful, and notes about flow, pain, medication, sleep, and stress can add context.
Limits of this estimate
- The calculator cannot predict an irregular cycle or explain a missed period.
- Bleeding while using hormonal contraception may not follow a natural menstrual cycle.
- Pregnancy, postpartum recovery, breastfeeding, perimenopause, illness, and stress can change timing.
Common questions
How should I use this estimate?
Use it as a planning starting point, then compare it with your own experience and any guidance from a qualified health professional.
Is this medical advice?
This calculator is an educational planning tool. It does not provide medical advice, determine whether bleeding is a period, or diagnose the reason for a timing or flow change.
What happens to what I enter?
The calculator uses the values in your current browser session to produce the result. It does not save them in browser storage.