Period Day
The period day calculator estimates the start date of your next period, your ovulation day, and your fertile window. For women with regular cycles, it is accurate around 85% of the time. The HekimDoktor calculator takes the start of your last period and your cycle length (if available) and gives you all the key dates for the coming month. Results save to the MenstrualCycle module, with push reminders enabled automatically.
Why HekimDoktor?
- ✓Next period, ovulation, and fertile window in one go
- ✓Opens the MenstrualCycle module for long-term tracking
- ✓Push reminders before and during your period
Frequently Asked Questions
Why is ovulation counted from mid-cycle rather than after the period ends?
Ovulation occurs 14 days before the next period (the luteal phase is fixed). This holds regardless of cycle length: in a 28-day cycle ovulation is on day 14, in a 30-day cycle on day 16.
What is the fertile window?
Five days before ovulation through ovulation day itself (six days total). Sperm can survive in the female body for up to five days, so fertility extends well before ovulation.
Is the calculation reliable for irregular periods?
For irregular cycles, accuracy drops to 50–60%. In that case, 3–6 months of tracking combined with ovulation test strips is more reliable. The HekimDoktor calendar module learns long-term patterns.
How is my data kept private?
It is encrypted with AES-256 under Turkish KVKK Art.6 (special category health data, equivalent to GDPR Art.9). It is never used even for anonymised analytics.