Due Date Calculator: Last Period, Conception Date, Ovulation or IVF?

Short answer: use the date that you know best. Most calculators start from the first day of your last period. If you know your conception or ovulation date, or you had IVF, use a tool that asks for that date, or ask your clinic. Any result is an estimate: your doctor or midwife gives the date that counts, and may adjust it after a scan.

The four common ways to calculate a due date

• Last period. You enter the first day of your last period. The calculator counts forward to an estimated due date. It is the most widely used method because most people know that date.
• Conception date. You enter the day you conceived, if you know it. The calculator counts from there instead.
• Ovulation date. If you track ovulation, you can use that date. It is close to conception, so it works like the conception method.
• IVF transfer date. With IVF, the transfer date and the age of the embryo at transfer are known exactly, so the due date is counted from them. Your clinic will usually give you the date directly.

Which method should you use?

• Regular, tracked cycle and a known last period: last period method.
• You know the conception or ovulation day: a conception or ovulation based tool.
• IVF or another fertility treatment: use the date from your clinic.
• Irregular cycles or you are not sure of any date: a calculator can only guess. Your care provider will date the pregnancy, sometimes with a scan.

Why two calculators can give different dates

Each tool starts from a different date and assumes a typical cycle length, so the results can be a few days apart. That is normal. Neither one is wrong; they are estimates built on different information. If your cycles are longer or shorter than average, a last-period calculation may not match one based on conception.

A due date is a guide, not an appointment

Babies arrive on their own schedule. Plan for a window around your estimated date rather than a single day, and ask your doctor or midwife what to expect in your own case. For anything about your health or your baby's, rely on your care team, not an online calculator.

Once you have a date: what to plan

1. 1Tell your care provider the date you used and ask them to confirm it.
2. 2Work out the dates around it: when to start the registry, when to have a baby shower. See when to have a baby shower.
3. 3Start a baby registry early so family can see what you need. The baby registry checklist helps you decide what to add.
4. 4Share the news. Use our ideas for announcing a pregnancy to family.

A playful way to share the due date

Family often wants to guess the arrival day. A simple game works well: everyone writes their guess and the closest one wins a small prize. Our baby due date guessing game shows you how. When you find out the baby's gender, you can reveal it live to everyone with a link or a 6-letter code, free and with no app.