Safe Period / Safe-Sex Day Estimator
Lower-risk and high-risk days, with honest limits. Free, private and instant.
How to use the Safe Period Estimator
- Pick first day of your last period.
- Enter average cycle length (days).
- Enter period length (days).
- Press Calculate to get an instant result with a colour scale, chart and plain-English explanation.
About the Safe Period Estimator
The safe period calculator uses the Standard Days Method for people with cycles of 26 to 32 days. It marks cycle days 8 to 19 as high risk and the rest as lower risk. There are no completely safe days, and this method does not protect against STIs.
Also known as: safe days calculator, calendar method calculator, rhythm method calculator, safe period for not getting pregnant.
Worked example
Dates in this example are worked out as if today were 5 Nov 2026.
- First day of your last period: 22 Oct 2026
- Average cycle length: 28 days
- Period length: 5 days
Today is cycle day: 15 (High-risk day: avoid unprotected sex). Day 15 falls in the Standard Days Method fertile window (days 8 to 19). Pregnancy is much more likely, so use a condom or avoid sex.
- High-risk days: Cycle days 8 to 19
- Lower-risk days: Days 1-7 and 20+
- Next period: 19 Nov 2026
- Typical-use failure: 12 in 100 per year
Formula and cut-offs
Standard Days Method: avoid unprotected sex on cycle days 8 to 19 (cycle length 26-32 days). Typical-use failure is about 12 pregnancies per 100 users per year.
Frequently asked questions
Are there really safe days to have sex?
No day is completely safe. Days outside the fertile window are lower risk, but pregnancy is still possible.
Does the calendar method prevent STIs?
No. Only condoms reduce the risk of STIs and HIV.
Who should not use the safe period method?
People with irregular cycles, cycles outside 26-32 days, recent childbirth, breastfeeding or recent hormonal contraception.
Sources and references
- World Health Organization - Family planning/contraception methods
- NHS - Contraception guide
- CDC - Sexually transmitted infections (STIs)
Written and checked by the MediHub editorial team against the sources above. Read how we build and review our calculators.
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Last updated . This calculator is for education only and is not medical advice. See the medical disclaimer.