Due Date Calculator
Work out your expected delivery date from your last period, your conception date or a dating scan.
Open calculator → Fertility planning
Ovulation & Fertile Window Calculator
Enter the first day of your last period and your usual cycle length to see when you are most likely to ovulate, and the six days each month when conception is most likely.
How to use it
- Pick the first day of bleeding of your most recent period — spotting the day before does not count.
- Set your average cycle length. If your cycles vary, use the length that happens most often, then treat the fertile window as approximate.
- Read the fertile window, not just the single ovulation day. The egg survives about 24 hours, but sperm can survive up to five days, so the days *before* ovulation matter most.
What it estimates — and what it cannot
- This calculator assumes you ovulate about 14 days before your next period. That holds for most regular cycles, but it is an average, not a measurement.
- Accuracy drops with irregular cycles, PCOS, thyroid problems, recent stopping of hormonal contraception, breastfeeding, significant stress or illness, and as you approach your forties.
- It cannot be used as contraception. Ovulation can shift by several days from one month to the next, even in women with regular cycles.
- If you want certainty rather than an estimate, follicular tracking on ultrasound at the hospital shows the actual growing follicle and the actual day of release.
When to see a specialist
See a fertility specialist after 12 months of regular, unprotected intercourse without a pregnancy — or after 6 months if you are 35 or older. Come sooner if your periods are irregular or absent, if you have known endometriosis, PCOS or blocked tubes, if you have had two or more miscarriages, or if there is a known problem with the male partner’s semen analysis.
Frequently asked questions
How does the ovulation calculator work?
It uses the luteal phase rule: in most women ovulation happens roughly 14 days before the next period starts. So it adds your cycle length to the first day of your last period to find the next period, then counts back 14 days. The fertile window is the five days before ovulation plus the day of ovulation itself, because sperm can survive several days inside the reproductive tract.
How accurate is it if my cycles are irregular?
Much less accurate. If your cycle varies by more than about four days from month to month, the predicted date can be out by a week or more. In that case ovulation predictor kits, basal body temperature charting, or — most reliably — follicular tracking by ultrasound will tell you far more than any calculator.
Can I use this to avoid pregnancy?
No. Please do not. Ovulation timing shifts, sperm survive up to five days, and pregnancies routinely happen on days a calculator calls "safe". Use a proper contraceptive method and speak to your gynecologist about which one suits you.
When should I take a pregnancy test?
A urine test is most reliable from the first day of a missed period, which is about 14 days after ovulation. Testing earlier often gives a false negative simply because hCG levels are still too low. A blood beta-hCG can detect pregnancy a few days earlier than urine.
How often should we have intercourse during the fertile window?
Every one to two days through the fertile window is enough. Daily is not harmful for most couples, but abstaining for long stretches to "save up" sperm does not help — it tends to reduce sperm motility.
Other calculators
IVF & FET Due Date Calculator
Due date after IVF, ICSI or frozen embryo transfer — from your transfer day or egg retrieval date.
Open calculator →Period Calculator
See when your next six periods are due, and check whether your cycle length is in the normal range.
Open calculator →Emergency? Call Us
24x7 emergency and labour support in Amravati.