Ovulation Calculator
Find your most fertile days and estimated ovulation date. Enter the first day of your last period and your average cycle length.
How to Use the Ovulation Calculator
Enter the year, month, and day of the first day of your last menstrual period, along with your average cycle length. The calculator estimates your ovulation date and the 6-day fertile window — the days you are most likely to conceive.
The Extended Calculator below shows a visual cycle calendar and a 3-month fertility forecast. The Professional Calculator adds multi-cycle analysis, a BBT charting reference, and a cervical mucus guide.
3-Month Forecast
| Cycle | Period | Fertile Window | Ovulation |
|---|---|---|---|
| Cycle 1 (current) | 01 Nov 2025 | 10 Nov – 16 Nov | 15 Nov 2025 |
| Cycle 2 | 29 Nov 2025 | 08 Dec – 14 Dec | 13 Dec 2025 |
| Cycle 3 | 27 Dec 2025 | 05 Jan – 11 Jan | 10 Jan 2026 |
How Ovulation Is Calculated
Ovulation Day: First day of LMP + (Cycle Length − 14)
Fertile Window: Ovulation Day − 5 days to Ovulation Day + 1 day
The luteal phase (ovulation to next period) is assumed to be 14 days — this is relatively consistent across women, while the follicular phase varies.
Example
LMP: 1 March, cycle length 28 days:
Ovulation = 1 March + (28 − 14) = 15 March
Fertile window = 10 March to 16 March
Next period = 1 March + 28 = 29 March
BBT Charting Reference (Basal Body Temperature)
What is BBT? Your body's lowest resting temperature, taken first thing each morning before any activity.
How to interpret:
- Pre-ovulation: 36.1–36.4°C (lower phase)
- Ovulation drop: Often a slight dip just before ovulation
- Post-ovulation rise: 36.4–37.0°C — confirms ovulation occurred
- Sustained rise 18+ days: May indicate pregnancy
BBT confirms ovulation after the fact — it does not predict it. Combine with LH testing for best results.
Cervical Mucus Guide
| Cycle Phase | Mucus Type | Fertility Signal |
|---|---|---|
| Period (D1–5) | Blood / none | Low |
| Post-period (D5–9) | Dry or sticky, white | Low |
| Pre-ovulation (D10–13) | Creamy, white/yellow | Medium |
| Fertile window | Clear, stretchy (egg white) | High |
| Post-ovulation | Thick, sticky, decreases | Low |