Ovulation Calculator
Work out the likely ovulation day and the fertile window from your last period and cycle length.
Ovulation Calculator
Likely ovulation day
17 October 2026
- Most fertile days12 Oct 2026 to 18 Oct 2026
- Next period expected31 October 2026
- Earliest useful pregnancy test31 October 2026
Works out in your browser. Nothing you type is sent anywhere.
In short: Ovulation Calculator
From the dates entered, ovulation is likely around 14 October 2026, with the most fertile days being 9 Oct 2026 to 15 Oct 2026. The next period would be expected around 28 October 2026, and a pregnancy test is only meaningful from about 28 October 2026. These are estimates from a calendar, not an observation.
What is Ovulation?
Ovulation is the day an egg is released, which falls roughly a fixed number of days before the next period rather than a fixed number after the last one.
How is Ovulation calculated?
The phase after ovulation is the steadier one, so ovulation is counted backwards from the expected next period rather than forwards from the last one. The fertile window covers the days before ovulation and the day after, because sperm survive for several days.
- last periodthe first day of your last period
- cycleyour usual cycle length in days
- lutealthe days between ovulation and the next period
A worked example
| First day of your last period | 30 September 2026 |
|---|---|
| Usual cycle length (days) | 28 |
| Luteal phase (days) | 14 |
| Result | |
| Likely ovulation day | 14 October 2026 |
| Most fertile days | 9 Oct 2026 to 15 Oct 2026 |
| Next period expected | 28 October 2026 |
| Earliest useful pregnancy test | 28 October 2026 |
Every figure in this table is produced by the same calculation the tool above runs.
How to use this ovulation calculator
- Enter the first day of your last period, not the day it ended.
- Enter your usual cycle length, counted from one first day to the next.
- Adjust the luteal phase only if you know yours from tracking.
- Read the fertile window rather than the single day.
Questions people ask
How reliable is a calendar estimate?
It is a reasonable starting point for a regular cycle and much less reliable for an irregular one, because it assumes the next period arrives on schedule. Ovulation can shift with illness, travel and stress. Ovulation predictor kits and basal temperature tracking observe what actually happened rather than predicting it.
Why is the fertile window several days long?
Because sperm can survive for several days in the reproductive tract, so intercourse before ovulation can still result in conception, while the egg itself survives less than a day. That is why the window runs up to ovulation and only just past it.
What if my cycles are irregular?
Then any calendar method, including this one, has wide error bars, and the figures here should be treated as rough. Tracking several cycles, or using predictor kits, gives a far better picture. Cycles that are persistently irregular are worth discussing with a doctor.
Is anything I type here saved or shared?
No. The calculation runs inside your browser, nothing is stored, and this tool will not put your dates into a shareable link or an image. Only the page's own address can be shared, never your dates.
Accuracy and sources
For general information. Not medical advice.
Checked by the Daytoolz team on 16 October 2026. How we check our tools.