Free Online Ovulation and Safe Days Fertility Calculator

Privacy-first, evidence-based cycle estimation tool.

Cycle Details

First Day of Last Period

Average Cycle Length (Days)

20-45 days

Period Duration (Days)

1-10 days

Data is processed in-memory only. No personal information is stored or transmitted.

Next Ovulation

Fertile Window

Next Period

Period

Ovulation

Fertile

Safe

Sun

Mon

Tue

Wed

Thu

Fri

Sat

Please select your last period date to generate your personalized fertility window and ovulation estimate.