Ovulation Calculator
Get an estimated fertile window and ovulation date as you type.
FREE - NO SIGN-UP - RUNS ON YOUR DEVICE
Your entries stay on your device
- Liveupdates as you type
- 0data uploaded
- 1clear result
- Freeno account needed
What you can count on
- 0data sent
- Calculations run in this browser
- Entries stay on this device
- Liveresult
- Figures update as values change
- Copy the summary when ready
- Clearmethod
- Inputs and formula basis shown
- Estimate, not medical advice
Ovulation Calculator at a glance
- Input
- Last period's first day, cycle length
- Output
- Ovulation, fertile window, next period
- Health notice
- Estimate, not medical advice
- Processing
- Runs locally in your browser
- Cycle length accepted
- 21–45 days
- How the dates are found
- Ovulation −14, window 6 days
- Price
- Free
- Account required
- No
How to use Ovulation Calculator
- 1
Enter your values
Enter the first day of the last period and cycle length.
- 2
Review the estimate
See estimated ovulation, fertile window and next period dates.
- 3
Copy the result
Use Copy result to save the displayed summary for your own notes.
Frequently asked questions
Is this result medical advice?
No. It is a general estimate based on the values and formula shown. A qualified health professional can interpret measurements for your circumstances.
Are my entries uploaded?
No. The calculation runs in your current browser tab, and the tool does not send the values to a server.
Why might my result differ elsewhere?
Methods, rounding and reference assumptions vary. Check the selected units and inputs, then treat the result as an estimate rather than a diagnosis.
Understanding the estimate
Enter the first day of the last period and cycle length. See estimated ovulation, fertile window and next period dates. This calculator provides an estimate, not medical advice.
- The result follows the method named in the tool and rounds figures for easy reading.
- Personal circumstances vary, so use the figure as a general reference and not a diagnosis.
Full specification
| Input | Enter the first day of the last period and cycle length. |
|---|---|
| Output | See estimated ovulation, fertile window and next period dates. |
| Health notice | This result is an estimate for general information and is not medical advice. |
| Processing | All calculations run locally in the current browser tab. |
| Cycle length accepted | 21 to 45 days. Anything outside that comes back as a message rather than a set of dates. |
| How the dates are found | Ovulation is 14 days before the next period. The fertile window runs from 5 days before it to 1 day after — six days. |
| Price | Free |
| Account required | No |
Keep going with the same files
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