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Ovulation & Fertile Window Calculator
Find the days you are most likely to conceive. Enter your last period and cycle length to see your fertile window on a calendar, your peak days, estimated ovulation, when to take a pregnancy test, and your due date if you conceive this cycle. Everything is worked out in your browser, nothing is stored.
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Estimated ovulation
Your fertile window on a calendar
Your next 6 cycles
If your cycle stays about the same, here are your upcoming fertile windows so you can plan ahead.
| Cycle starts (period) | Fertile window | Ovulation | Test from |
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How this ovulation calculator works
Ovulation, when an ovary releases an egg, usually happens about 14 days before your next period starts, not 14 days after your last one. So the calculator counts forward to your next period using your cycle length, then steps back by your luteal phase (14 days by default) to estimate ovulation.
Your fertile window is the day of ovulation plus the five days before it, about six days in total. That is because sperm can survive in the body for up to five days, while the egg only lives for about 12 to 24 hours after it is released. The two or three days leading up to and including ovulation are your peak days, when your chance of conceiving is highest.
If your cycles are regular, this is a good starting point. If they are irregular, the date is less reliable, so lean on the ovulation signs below.
Signs you are ovulating
Egg-white cervical mucus
Around ovulation, discharge becomes clear, slippery and stretchy, like raw egg white. This is the most fertile type and the easiest sign to spot.
A small rise in temperature
Your basal body temperature (taken first thing each morning) rises by about 0.4 to 1.0 degrees F just after ovulation, confirming it has happened.
A positive ovulation test
Ovulation predictor kits detect the surge in luteinising hormone (LH) that happens 24 to 36 hours before ovulation, the green light for your peak days.
Mild twinges or other signs
Some women feel a one-sided ache (mittelschmerz), light spotting, a higher sex drive, breast tenderness or mild bloating mid-cycle.
Tips to boost your chances
- Time it right. Have sex every one to two days through your fertile window, especially on your peak days. Daily or alternate-day is fine for most couples.
- Do not wait for a positive test to start. By the time an ovulation test is positive you are already near the end of the window, so begin a few days earlier.
- Track more than dates. Combine this calculator with cervical mucus and, if you like, basal body temperature or an ovulation kit for a clearer picture.
- Look after the basics. A balanced diet, a healthy weight, folic acid, less alcohol and not smoking all support conception, for both partners.
- Give it time. About 8 in 10 couples conceive within a year of trying. See a doctor sooner if you are over 35 or have irregular or absent periods.
Irregular cycles and when to see a doctor in Singapore
If your cycle length changes a lot from month to month, a single ovulation date is hard to pin down. Conditions like PCOS or thyroid problems can affect ovulation. Tracking cervical mucus and using ovulation test kits over a few cycles usually works better than the calendar alone.
In Singapore, speak to your GP, a polyclinic, or an O&G or fertility specialist (for example at KKH, NUH or a private fertility clinic) if you are under 35 and have been trying for 12 months, 35 or older and trying for 6 months, or if your periods are very irregular, very painful or absent. Getting checked early keeps your options open.
Frequently asked questions
When am I most fertile?
You are most fertile on the two to three days leading up to and including ovulation, the peak days highlighted above. Your wider fertile window is the six days ending on ovulation day.
When does ovulation happen after my period?
It depends on your cycle length, because ovulation is about 14 days before your next period, not a fixed number of days after your last one. On a 28-day cycle that is around day 14; on a 35-day cycle it is closer to day 21.
How many days after my period am I most fertile?
On a typical 28-day cycle with a 5-day period, your fertile window often falls a few days after bleeding ends (roughly cycle days 9 to 14). On longer cycles it is later. Use the calendar above for your own dates.
Can I get pregnant outside my fertile window?
It is much less likely but not impossible, because cycles and ovulation timing vary. If you are avoiding pregnancy, do not rely on this calculator as contraception.
When should I take a pregnancy test?
A home test is most reliable from about the day your period is due, roughly 14 days after ovulation. Testing earlier can give a false negative. We show your earliest sensible test date above.
How accurate is an ovulation calculator?
It is a useful estimate for regular cycles, but it assumes you ovulate on schedule, which not everyone does. Pair it with ovulation signs for better accuracy.
Can I have a period and still not ovulate?
Yes. Anovulatory cycles (bleeding without releasing an egg) can happen occasionally and are more common with PCOS, around puberty and approaching menopause. If they are frequent, see a doctor.
How do I calculate my ovulation day myself?
Subtract 14 from your cycle length to estimate the day you ovulate, counting from the first day of your period. For a 30-day cycle that is around day 16. Your luteal phase may differ, which is why we let you adjust it.
