Ovulation and fertility calculator
Estimate your fertile days and ovulation date from cycle length and last period. Shows multiple upcoming cycles.
- Free, no sign-up
- No data stored
- Reviewed 2026-01-15
Your details
Results
- Fertile window
- 31 Aug – 6 Sep
- Next period
- 19 Sep 2026
- Implantation window
- 11 Sep – 17 Sep
- Test from
- 19 Sep 2026
- Estimated due date
- 29 May 2027
Test note
If conception note
Cycles table
| Cycle | Period start | Fertile window | Ovulation | Next period |
|---|---|---|---|---|
| 1 | 22 Aug 2026 | 31 Aug – 6 Sep | 5 Sep 2026 | 19 Sep 2026 |
| 2 | 19 Sep 2026 | 28 Sep – 4 Oct | 3 Oct 2026 | 17 Oct 2026 |
| 3 | 17 Oct 2026 | 26 Oct – 1 Nov | 31 Oct 2026 | 14 Nov 2026 |
| 4 | 14 Nov 2026 | 23 Nov – 29 Nov | 28 Nov 2026 | 12 Dec 2026 |
| 5 | 12 Dec 2026 | 21 Dec – 27 Dec | 26 Dec 2026 | 9 Jan 2027 |
| 6 | 9 Jan 2027 | 18 Jan – 24 Jan | 23 Jan 2027 | 6 Feb 2027 |
Ovulation note
About the Ovulation Calculator
Enter the first day of your last period and your average cycle length to estimate ovulation and the fertile window for the next several cycles. The fertile window typically spans 5 days before ovulation plus the day of ovulation itself.
Ovulation is estimated as cycle length minus the luteal phase (default 14 days). If you know your luteal phase length, adjust it for better accuracy.
How to use the Ovulation Calculator
- Enter the first day of your last menstrual period.
- Set your average cycle length.
- Optionally adjust the luteal phase length.
- Choose how many cycles to display.
- View estimated ovulation dates and fertile windows.
Frequently asked questions
How accurate is this?
It provides an estimate based on averages. Real ovulation can vary by several days between cycles. Combine with other signs (temperature, cervical mucus, OPKs) for better tracking.
What is the luteal phase?
The time between ovulation and the start of the next period. It is typically 12–14 days and fairly consistent for each individual.
Can irregular cycles be tracked?
For very irregular cycles, predictions become less reliable. Use the shortest recent cycle as a conservative estimate.