Is ovulation always 14 days before the next period?

The luteal phase (ovulation → next period) is more consistent at about 14 days than the follicular phase (period → ovulation). In a 30-day cycle, ovulation is closer to day 16; in a 26-day cycle, closer to day 12. The tool counts back 14 days from predicted next period for this reason.

Why is the fertile window six days long when I only ovulate once?

Sperm can survive in the reproductive tract for up to 5 days, so intercourse from 5 days before ovulation through ovulation day itself can all result in conception. The egg itself is viable for ~24 hours.

Can I use this for birth control?

No. Even in regular cycles, ovulation can shift by 3–4 days due to stress, illness, or travel. The failure rate of rhythm-based methods is 12–24% per year. For contraception, use a clinically reviewed method.

I've already conceived — what do I use?

Switch over to the pregnancy calculator, which takes your LMP and returns a due date (Naegele's rule: LMP + 280 days) plus your current week and trimester.

Health & Fitness · Free tool

Ovulation Calculator

Find your estimated ovulation date and fertile window from the last period and cycle length. Free, private, 100% in-browser.

Updated June 2026

First day of last periodCycle length (days)

Ovulation day

Jun 15, 2026

Fertile window

Jun 10 – Jun 15, 2026

Next period

Jun 29, 2026

Cycle length

28 days

Cycle	Fertile window	Ovulation	Next period
#1	Jun 10 – Jun 15, 2026	Jun 15, 2026	Jun 29, 2026
#2	Jul 8 – Jul 13, 2026	Jul 13, 2026	Jul 27, 2026
#3	Aug 5 – Aug 10, 2026	Aug 10, 2026	Aug 24, 2026

How it works

Ovulation is estimated at (cycle length − 14) days after the first day of your period.
The fertile window covers the 5 days before ovulation plus ovulation day itself.
Estimates only — track basal temp or use LH tests for accuracy.

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What it does

Find your most fertile days from the date of your last period and your average cycle length. The tool estimates ovulation (around 14 days before your next period), the six-day fertile window leading up to it, and the predicted start of your next three cycles — useful whether you're trying to conceive or planning around your cycle.

This is a rhythm-based estimate; real ovulation varies by a few days from cycle to cycle. For higher accuracy combine with basal body temperature tracking or ovulation test strips. If you've already conceived, switch over to pregnancy calculator for due-date and week math.

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Example input & output

Input

Last period started: Apr 1
Average cycle: 28 days

Output

Predicted ovulation: Apr 15 (Day 14)
Fertile window: Apr 10–Apr 15
Next period: Apr 29

Shifting the cycle length to 30 days moves ovulation to Day 16 (Apr 17). The 6-day fertile window always ends on ovulation day.

How to use it

Enter the first day of your last period.
Enter your average cycle length (default 28 days).
Review your predicted ovulation day and fertile window.
Plan around the next three predicted cycles shown below.

When to use this tool

Planning around your most fertile window (typically day 10–14 of a 28-day cycle).
Tracking cycle regularity across several months to spot patterns.
Estimating when your next period is due for travel, events, or workouts.
Combining with basal body temperature or LH strips for higher-confidence timing.

When not to use it

Reliable contraception — rhythm-based estimates are not a birth-control method.
Irregular cycles where length varies by more than ±5 days — ovulation tests are more reliable here.
Medical fertility workup — see a clinician for AMH, ultrasound, and lab-based ovulation confirmation.
Post-hormonal-contraception cycles (IUD removal, pill stoppage) while cycles are still stabilizing.

Frequently asked questions

Is ovulation always 14 days before the next period?: The luteal phase (ovulation → next period) is more consistent at about 14 days than the follicular phase (period → ovulation). In a 30-day cycle, ovulation is closer to day 16; in a 26-day cycle, closer to day 12. The tool counts back 14 days from predicted next period for this reason.
Why is the fertile window six days long when I only ovulate once?: Sperm can survive in the reproductive tract for up to 5 days, so intercourse from 5 days before ovulation through ovulation day itself can all result in conception. The egg itself is viable for ~24 hours.
Can I use this for birth control?: No. Even in regular cycles, ovulation can shift by 3–4 days due to stress, illness, or travel. The failure rate of rhythm-based methods is 12–24% per year. For contraception, use a clinically reviewed method.
I've already conceived — what do I use?: Switch over to the pregnancy calculator, which takes your LMP and returns a due date (Naegele's rule: LMP + 280 days) plus your current week and trimester.

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