Fertility Window Calculator

Calendar method: ovulation = cycle length − 14 days (average). LH surge kits detect surge 24–36 hrs before ovulation (most accurate). Basal body temperature rise (0.5°C) confirms ovulation post-hoc.

Yes. 28-day cycles: simple prediction. 21–35 days normal but unpredictable. Track 3 months minimum to establish pattern. Apps (Clue, Flo) help predict best.

Irregular cycles, anovulation (no ovulation), poor egg/sperm quality, timing (intercourse every 2–3 days throughout cycle > precise timing), age (female fertility drops 35+).