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Conception Date Calculator
Work out roughly when you conceived from your due date, last period, baby's birthday, a dating scan or an IVF transfer. See your likely conception window, the days intercourse may have led to conception, how far along you are, and your estimated due date. A planning estimate, not a paternity test.
Estimated conception date
How we worked this out
Conception happens at ovulation, when sperm meets egg. Because a pregnancy is dated from the first day of your last period, but you only conceive about two weeks later, conception is roughly 38 weeks (266 days) before your due date. Here is what each option does:
- From your due date: conception = due date minus 266 days.
- From your last period: conception = last period plus (cycle length minus 14 days), because you ovulate about 14 days before your next period.
- From your baby's birthday: we count back using how many weeks your baby was born at, so an early or late birth does not skew the date.
- From a dating scan: we use the gestational age the scan gave you to find your dating last period, then add about 14 days to reach conception.
- From IVF: conception is the day the egg was fertilised, which is the transfer date minus the embryo's age (3, 5 or 6 days).
Fertilisation, conception and implantation
These three are not the same day. Conception (fertilisation) happens within about a day of ovulation. The fertilised egg then travels to the womb and implants about 6 to 12 days later, which is when pregnancy hormones start to rise and a test can eventually pick them up.
Why it is a window, not one exact day
Sperm can survive for up to five days inside the body, while the egg lives only about 12 to 24 hours after it is released. So intercourse on any of several days could have led to conception. That is why we show a likely intercourse window rather than a single date, and why ovulation timing naturally varies from cycle to cycle.
Using this for paternity questions
This calculator can give a rough idea, but it cannot prove who the father is. Conception timing varies by several days, and only an early ultrasound (or a DNA test after birth) can date a pregnancy accurately. Please do not rely on these dates for any legal or relationship decision.
Confirming the date in Singapore
If you want a reliable conception or due date, an early dating scan is the gold standard. In Singapore these are usually done between 7 and 14 weeks at your O&G or at KKH, NUH or SGH, and are accurate to within about a week. Once you have a confirmed due date you can plan ahead with our due-date calculator and work out costs and grants with our Baby Bonus and cost estimator.
Frequently asked questions
How is my conception date calculated?
Conception is estimated as about 266 days (38 weeks) before your due date, or roughly 14 days after the first day of your last period on a 28-day cycle. The exact day depends on when you ovulated.
How accurate is a conception date?
It is an estimate, not an exact day, because ovulation timing varies and sperm can survive for several days. Treat the result as a window. An early dating scan is the most accurate method.
Can I use this to work out paternity?
No. It can suggest a likely window but cannot prove paternity. Conception dates can be out by several days, so only a dating ultrasound or a post-birth DNA test can confirm timing.
How far along am I based on my conception date?
Add about two weeks to the time since conception to get your gestational age, which is how pregnancy is normally counted. The calculator shows your current weeks and days above.
What if my cycle is not 28 days?
Choose the last-period option and enter your cycle length. Because ovulation is about 14 days before your next period, a longer cycle means you conceived later, and a shorter cycle earlier.
What if my baby was born early or late?
Use the baby's birthday option and set how many weeks your baby was born at. Counting back a flat 40 weeks from a premature birth would put conception too early, so this keeps it accurate.
When can I take a pregnancy test after conception?
Most home tests are reliable from around the day your period is due, which is about two weeks after conception. Testing earlier can give a false negative.
Is the conception date the same as my last period?
No. Your last period comes first, then you ovulate and conceive about two weeks later. Pregnancy is dated from the period, which is why you can be "two weeks pregnant" before you actually conceived.
