Safe period calculator
⚠️ NOT a contraceptive method. Calendar-based "safe days" fail for 12–24 in 100 couples per year of typical use (WHO/ACOG). If you do not want to become pregnant, use reliable contraception.
🔒 Calculated locally — your dates never leave your device
The calendar marks the higher-risk fertile window (5 days before ovulation through 1 day after) and the relatively lower-risk days around it, based on your average cycle.
Why it fails: ovulation can move with stress or illness, sperm survive up to ~5 days, and many cycles are not perfectly regular. If avoiding pregnancy matters to you, choose a reliable method (condoms, pill, IUD) — talk to a doctor.
Frequently asked questions
How safe is the safe period really?
With perfect calculation the calendar method still fails about 5% per year; with typical real-world use, 12–24%. That is roughly 1 unplanned pregnancy per 4–8 couples per year — far below condoms, the pill or an IUD.
Which days are the "safe" ones?
Days outside the fertile window (5 days before ovulation to 1 day after) are relatively lower risk. But because ovulation shifts, no calendar day is truly guaranteed safe.
What if we had unprotected sex during the fertile window?
If you want to avoid pregnancy, ask a doctor or pharmacist about emergency contraception as soon as possible — it is a backup, not a routine method.
Related reading
Is the “safe period” reliable for avoiding pregnancy?
No. The “safe period” (calendar or rhythm method) is not reliable contraception. Even calculated perfectly it fails about 5% of the time per year; with typical real-world use, 12–24 in 100 people become pregnant within a year — because ovulation shifts and sperm survive for days.
Read more →Can you get pregnant on your period?
Yes — it is less likely, but possible. Sperm can survive up to about 5 days, so if you have a short cycle and ovulate early, sperm from sex during your period can still be around when an egg is released. There is no truly “no-risk” day with calendar timing.
Read more →Birth control methods compared
The most reliable birth control methods are long-acting ones — the implant and the IUD — with under 1% failure per year. The pill and condoms work well when used correctly, while calendar-based “safe days” fail for 12–24 in 100 people per year.
Read more →References
- WHO/JHU – Family Planning: A Global Handbook for Providers, ch. Fertility Awareness Methods
- ACOG – Fertility Awareness-Based Methods (effectiveness data)
- CDC – Contraception: typical-use failure rates