Conception Date Calculator: When Did I Conceive?
Free conception date calculator: find your most likely conception date from your due date, last period, IVF transfer or ultrasound, with the days sex could have led to the pregnancy and your estimated ovulation date. Private and quick.
🔒 Private by design: your dates are saved only in this browser (never uploaded, no account) and are shared by the three calculators below.
More options: period length, luteal phase, ovulation (LH) test
Your chances, day by day
Chance of pregnancy from sex on each day, for a typical couple. The two days before ovulation and ovulation day are the peak. Source: Wilcox, Weinberg & Baird, New England Journal of Medicine 1995 (129 couples, 625 cycles). Ovulation can move by a few days, which is why the whole window counts.
Your cycle log
Add the first day of each period you remember. With two or more, the calculator uses your own average instead of the textbook 28 days, and tells you how regular you are.
Upcoming periods
Calendar
Tap a day for details.
Next six cycles
Key dates
Week-by-week calendar (weeks 1–42)
Day by day after ovulation
Week by week
These are estimates from averages, not medical advice or contraception. Bodies vary and cycles change with stress, illness, breastfeeding and age. Talk to a doctor or midwife about your own situation, especially if your cycles are very irregular or you have been trying for 12 months (6 if you are over 35).
Conception date calculator
Work backwards from your due date, the first day of your last period or the age of the pregnancy to find the most likely conception date, the days when sex could have led to the pregnancy, and your estimated ovulation date. It also shows the equivalent last-period date doctors use to count your weeks.
How it works
- Conception is about 266 days (38 weeks) before the due date, which is about two weeks after the first day of your last period in a 28-day cycle.
- Sperm can live up to 5 days and the egg about a day, so sex in the five days before ovulation and on ovulation day can all lead to pregnancy. The calculator shows that whole window.
- If your cycle is longer or shorter than 28 days, enter it and the date moves with it.
Questions
How accurate is an estimated conception date?
It is an estimate of a few days either way. A due date from an early ultrasound is the most accurate base. Dates from the last period assume you ovulated on a typical day for your cycle length.
Why does my doctor say I am two weeks further along than my conception date suggests?
Pregnancy weeks are counted from the first day of the last period, about two weeks before conception. A baby conceived on a given date is “2 weeks pregnant” on that day.
Trying to conceive? Use the ovulation calculator to find your fertile window.