Period and ovulation calculator: both dates in one place
Next period: Friday, November 13
That’s in 18 days.
- Fri, Nov 13 – Tue, Nov 17
- Fri, Dec 11 – Tue, Dec 15
- Fri, Jan 8 – Tue, Jan 12
- Fri, Feb 5 – Tue, Feb 9
- Fri, Mar 5 – Tue, Mar 9
- Fri, Apr 2 – Tue, Apr 6
🔒 Calculated in your browser. Nothing you type is sent or stored. Estimates only: cycles vary.
A period and ovulation calculator starts from the first day of your last period. Add your cycle length to get your next period; count back 14 days from that to estimate ovulation. With a 28-day cycle starting 1 May, the next period is due 29 May and ovulation falls around 15 May, with fertile days from about 10 to 16 May.
How the period and ovulation calculator works
Your period and your ovulation are two ends of the same cycle. Ovulation happens first; if no pregnancy follows, your period starts about two weeks later. So the calculator only needs three things from you:
- The first day of your last period (day 1 is the first day of real bleeding, not spotting).
- Your usual cycle length, from day 1 of one period to the day before the next.
- How many days you usually bleed.
It then shows your next period date and how many days away it is, the start and end dates of your next six periods, and a calendar of your current cycle colored by phase, with the fertile days highlighted and a sun on your estimated ovulation day. Need ovulation dates for the next few months? The ovulation calendar lays out three cycles.
Everything is calculated in your browser. Nothing you type is sent to us or saved anywhere.
Period and ovulation dates by cycle length
Counting day 1 as the first day of your period, here is roughly where ovulation and the next period fall:
| Cycle length | Ovulation around | Fertile days | Next period starts |
|---|---|---|---|
| 21 days | day 7 | days 2 to 8 | day 22 |
| 24 days | day 10 | days 5 to 11 | day 25 |
| 28 days | day 14 | days 9 to 15 | day 29 |
| 30 days | day 16 | days 11 to 17 | day 31 |
| 32 days | day 18 | days 13 to 19 | day 33 |
| 35 days | day 21 | days 16 to 22 | day 36 |
Notice that only the first half of the cycle changes. The stretch from ovulation to your next period, the luteal phase, stays at about 12 to 14 days for most people. That's why the calculator counts back from the next period rather than forward from day 14.
Worked example
Your last period started on 1 May, your cycles are 28 days, and you bleed for 5 days. The calculator shows:
- Period: 1 to 5 May.
- Fertile window: about 10 to 16 May, most fertile on 13, 14 and 15 May.
- Estimated ovulation: around 15 May, 14 days before the next period (cycle day 14 or 15, depending on how you count).
- Next period: 29 May, then about every 28 days after that.
Why your period doesn't move ovulation
A longer or shorter period doesn't shift ovulation: a 7-day period and a 3-day period in a 28-day cycle both point to ovulation around day 14. What moves ovulation is the follicular phase, the time an egg takes to mature. Stress, illness, travel, intense exercise, coming off the pill, breastfeeding and conditions like PCOS can all stretch it. When ovulation is late, your period is late too.
How accurate is it?
The calculator uses one average, but real cycles vary. In a study of more than 600,000 cycles, average cycle length moved by a few days from month to month even for people who felt regular, and ovulation day varied more than people expect. Treat each date as the middle of a window. If your cycles are irregular, our ovulation calculator for irregular periods uses your shortest and longest cycles instead.
Your body gives clues to check against the dates: clear, stretchy discharge and sometimes a twinge of ovulation pain near ovulation, then breast tenderness, bloating or mood changes in the week before your period. Many people feel their best, most social days around ovulation and their most sensitive days just before bleeding starts.
When to talk to a doctor
See a doctor if your cycles are regularly shorter than 21 days or longer than 35, if your period stops for 3 months, if you bleed between periods or after sex, if periods are very heavy or painful, or if you've been trying to conceive for a year (6 months if you're 35 or older). These dates are estimates and are not a method of contraception.
Frequently asked questions
How many days after my period do I ovulate?
It depends on your cycle length. In a 28-day cycle with a 5-day period, ovulation is usually around 9 days after your period ends; in a 24-day cycle it can be just 5 days after.
Do you ovulate 14 days after your period?
Not exactly. Ovulation is about 14 days before your next period, not 14 days after your last one. In a 28-day cycle both happen to land around day 14.
Can you ovulate during your period?
It's rare, but with very short cycles your fertile window can begin while you're still bleeding. That's one reason sex during your period can lead to pregnancy.
Is a period and ovulation calculator accurate for irregular cycles?
Less so, because it relies on an average. Use your range of cycle lengths, or confirm with ovulation tests and body signs.
Sources
- NHS: Fertility in the menstrual cycle
- NHS: Periods
- Bull JR et al. Real-world menstrual cycle characteristics of more than 600,000 menstrual cycles. npj Digital Medicine (2019)
- Cleveland Clinic: Ovulation
This page is for information only and isn’t medical advice. If something worries you, please talk to a doctor.
Keep reading
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