Ovulation Calculator
Find your ovulation date, fertile window, and next period based on your cycle. Covers the next 3 cycles so you can plan ahead. Completely private, nothing leaves your browser.
Your cycle
Typical: 21–45 days
Typical: 3–7 days
14
days to ovulation
28
days to next period
Cycle 1, key dates
Period
Oct 31, 2026 – Nov 4
5 days
Fertile window
Nov 9, 2026 – Nov 15
7 days, highest chance of conception
Ovulation day
Nov 14, 2026
Peak fertility, egg viable ~24 hours
Next period
Nov 28, 2026
Cycle timeline, day by day
3-cycle overview
| Cycle | Period starts | Fertile window | Ovulation | Next period |
|---|---|---|---|---|
| Cycle 1 | Oct 31, 2026 | Nov 9 – Nov 15 | Nov 14, 2026 | Nov 28, 2026 |
| Cycle 2 | Nov 28, 2026 | Dec 7 – Dec 13 | Dec 12, 2026 | Dec 26, 2026 |
| Cycle 3 | Dec 26, 2026 | Jan 4 – Jan 10 | Jan 9, 2027 | Jan 23, 2027 |
⚠️ Medical disclaimer
This calculator uses the standard calendar method and assumes a regular cycle. It is not a substitute for medical advice, ovulation tests, or fertility treatment. Irregular cycles reduce prediction accuracy. Consult a healthcare provider for fertility planning.
How to use the ovulation calculator
Three inputs, three cycles of predictions. Takes under a minute.
- 01
Enter the first day of your last period
This is day 1 of your cycle: the first day of actual bleeding, not spotting. If you're not sure of the exact date, use your best estimate.
- 02
Set your cycle and period length
The average cycle is 28 days (range: 21–45). Period length is typically 3–7 days. If your cycle varies, use your average over the last 3–6 months.
- 03
Read your fertile window and ovulation date
The calculator shows your period, fertile window, ovulation day, and next period start for 3 upcoming cycles. Switch between cycles using the tabs.
What people use this for
Trying to conceive
The fertile window (5 days before ovulation + ovulation day) is when conception is most likely. Sperm can survive up to 5 days, so timing intercourse in this window maximises the chance.
Tracking your cycle for general health
Knowing when your period is due helps with planning, managing PMS symptoms, and spotting irregularities. A cycle that's consistently shorter than 21 days or longer than 45 days is worth discussing with a doctor.
Natural family planning
The calendar method can be used to identify fertile days to avoid. It's less reliable than hormonal contraception (typical use failure rate is around 24% per year) and works best with regular cycles.
Preparing for a fertility appointment
Doctors often ask for cycle history. Having 3–6 months of cycle data (start dates, length, period duration) makes the appointment more productive.
How the dates are estimated
The calculator assumes the second half of the cycle, the luteal phase, lasts 14 days, which is the textbook average. So ovulation is placed 14 days before the next expected period, and the fertile window runs from 5 days before ovulation to 1 day after, because sperm can survive up to about 5 days and the egg about a day.
| Cycle length | Estimated ovulation | Fertile window |
|---|---|---|
| 24 days | Day 10 | Days 5 to 11 |
| 28 days | Day 14 | Days 9 to 15 |
| 32 days | Day 18 | Days 13 to 19 |
| 35 days | Day 21 | Days 16 to 22 |
That's why a longer cycle moves ovulation later, not the period earlier. Day 1 is the first day of bleeding. The results show the next few cycles, each one simply the same length after the last.
Limits worth knowing
- Calendar estimates assume regular cycles. Ovulation can shift by several days from cycle to cycle, and the luteal phase varies between people, often from about 10 to 16 days.
- For a better estimate, combine it with ovulation test kits, which detect the hormone surge a day or two before ovulation, or with basal body temperature tracking.
- It isn't a method of contraception. The fertile window is an estimate, and relying on it to avoid pregnancy fails often.
- Irregular cycles, recent pregnancy, breastfeeding, PCOS or stopping hormonal contraception make calendar predictions much less reliable. A doctor can help if you've been trying to conceive for a year, or six months if you're over 35.