Ovulation and fertile window
Ovulation ~14 days before next period, not after last. Fertile window 5 days before + ovulation day =6 days due to sperm survival and egg lifespan.
TL;DR
- Next period = LMP + cycle length
- Formulas: Ovulation = LMP + (Cycle -14) days | Fertile = Ovulation ±5/1
- LMP Jan1 28
How it works
Next period = LMP + cycle length. Ovulation = next period -14 days = LMP + (cycle-14). Fertile = ovulation -5 to +1 days.
The math
Cycle 28 → ovulation LMP+14. Cycle 32 → LMP+18. LMP Jan1 28 → ovulation Jan15, fertile Jan10-16.
Subtract 14 from next period, not add 14 to LMP blindly.
Examples
LMP Jan1 28
- Ovulation Jan15
- Fertile Jan10-16
- Next Jan29
Cycle 32
- Ovulation LMP+18
When to use it
✦ Conception
Time intercourse.
✦ Contraception awareness
Avoid window (not standalone).
⚠ Common mistakes
- Assuming day 14 always
- Ignoring cycle variability
FAQ (6)
How accurate is this?
Calendar method is an estimate. Confirm with LH tests or temperature if timing is critical.
Can I get pregnant outside fertile window?
Very unlikely. Sperm lives up to 5 days, egg about 12-24 hours after ovulation.
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Sources & References
⚠ Health Disclaimer
This tool provides estimates for informational purposes only and does not constitute medical, veterinary, or professional advice. Always consult a qualified healthcare professional before making decisions about your health or treatment.