Ovulation Calculator
From the first day of your last period and your cycle length, find your likely ovulation day, fertile window and next period, for three cycles ahead.
From the first day of one period to the first day of the next.
Days from ovulation to the next period. Leave at 14 unless you track it.
Likely ovulation
26 November 2026 Thursday
- Fertile window
- 21 November 2026 to 27 November 2026
- Next period due
- 10 December 2026
With a 28-day cycle, you are most likely to ovulate around Thursday, 26 November 2026. Your most fertile days run from 21 November 2026 to 27 November 2026.
How it's worked out
- Next period
12 November 2026 + 28 days10 December 2026 - Ovulation
next period − 14-day luteal phase26 November 2026 - Fertile window
5 days before ovulation to 1 day after (sperm live up to 5 days; the egg about 1)21 November 2026 to 27 November 2026
The next three cycles
| Cycle | Fertile window | Ovulation | Next period |
|---|---|---|---|
| 1 | 21 Nov to 27 Nov | 26 Nov | 10 Dec |
| 2 | 19 Dec to 25 Dec | 24 Dec | 7 Jan |
| 3 | 16 Jan to 22 Jan | 21 Jan | 4 Feb |
- An estimate from the calendar, not a test. Cycles shift with stress, illness and travel; ovulation tests or temperature tracking are more exact. Not a method of contraception.
How it works
Ovulation = last period + cycle length − luteal phase · Fertile window = 5 days before ovulation to 1 day after
The luteal phase, from ovulation to the next period, is fairly steady at about 14 days. Most of the variation in cycle length happens before ovulation.
Worked example
A period that started on 1 October in a 28-day cycle means the next is due on 29 October. Ovulation is likely around 15 October, and the fertile window runs from 10 to 16 October.
Questions people ask
When do I ovulate?
Usually about 14 days before your next period starts. Counting the first day of your period as day 1, in a 28-day cycle that's around day 15; in a 32-day cycle, around day 19.
What is the fertile window?
The 5 days before ovulation and the day after it. Sperm can live up to 5 days, and the egg about a day.
How accurate is this?
It's a calendar estimate. Cycles shift with stress, illness and travel, so ovulation tests or temperature tracking are more exact. It is not a method of contraception.
About this calculator
Formula and rules last checked 25 October 2026Written and tested by the CalculatorDex teamReport a problem