Conception Calculator
This calculator is for informational purposes only and is not a substitute for professional medical advice. Consult a healthcare provider for personal health decisions.
Ovulation ≈ LMP + (cycle length − 14); fertile window ±5 days
How Conception Timing Is Estimated
Planning pregnancy benefits from knowing when ovulation and the fertile window occur. This calculator starts from the first day of your last menstrual period (LMP), cycle length, and period duration to project three cycles of key dates on a color-coded calendar.
Ovulation is estimated as LMP + (cycle length − 14) — the classic luteal-phase assumption. For a 28-day cycle starting January 1, ovulation falls around day 14 (January 15). The fertile window spans ovulation − 5 through ovulation + 1 (seven days total) accounting for sperm survival and egg viability.
Peak fertility days are ovulation − 2, −1, and ovulation day. Implantation typically occurs ovulation + 6 to + 12. The two-week wait runs from after ovulation + 1 until the test window begins. Pregnancy tests are most reliable from ovulation + 12 to + 14 when hCG levels are detectable.
Cycle length varies — stress, illness, and hormonal changes shift ovulation. This tool complements (not replaces) ovulation tests, basal body temperature, and medical fertility guidance. See our ovulation and period calculators for related tracking.
Examples
| Example | Result |
|---|---|
| 28-day cycle, LMP Jan 1 | Ovulation ~Jan 15; 7-day fertile window |
| 30-day cycle | Ovulation at day 16 offset |
| Peak fertility | 3 days centered on ovulation |
Frequently asked questions
Peak fertility covers the two days before ovulation and ovulation day itself. The broader fertile window includes five days before through one day after ovulation.
Home tests are most reliable from about 12–14 days after ovulation, or after a missed period. Testing too early may produce false negatives.
This page adds implantation timing, two-week wait, test windows, peak fertility days, and a 3-cycle calendar with six color-coded day types.