Estimate your due date from your last menstrual period, conception date or IVF transfer — plus how far along you are today and the milestones ahead.
Estimates only — your provider may adjust your due date after an ultrasound. Nothing you enter leaves your browser.
This calculator uses the same method most doctors and midwives use: Naegele's rule. Take the first day of your last menstrual period (LMP), add 280 days — 40 weeks — and you have your estimated due date. It sounds odd to start counting before you were actually pregnant, but that's how pregnancy is dated everywhere: the LMP is an easy, memorable starting point, while the exact day of conception usually isn't known.
Naegele's rule assumes a 28-day cycle with ovulation on day 14. If your cycles run longer or shorter, ovulation — and therefore your due date — shifts too. That's why the calculator asks for your average cycle length and nudges the date by one day for every day your cycle differs from 28. A 32-day cycle, for example, pushes your due date about 4 days later than the standard calculation.
Here's the honest answer: your due date is a well-informed guess, not an appointment. Only around 4 to 5 percent of babies are born on their exact due date. Most arrive sometime in the two weeks before or after it. Think of your due date less as a deadline and more as the middle of a "due month."
That's also why ACOG (the American College of Obstetricians and Gynecologists) moved away from a single "term" label. Full term is now defined as 39 weeks 0 days through 40 weeks 6 days. Birth at 37–38 weeks is called early term, 41 weeks is late term, and 42 weeks or beyond is post-term. If your baby hasn't arrived by the due date, that's normal — many first babies come a little late.
All three methods in this calculator land on the same underlying timeline — they just start counting from different points:
At your first ultrasound — often between 8 and 13 weeks — the sonographer measures your baby from head to bottom (the crown–rump length) and compares it to growth charts. In the first trimester, embryos grow at a remarkably uniform rate, which makes this measurement the most accurate way to date a pregnancy.
If the ultrasound estimate differs enough from your LMP-based date, your provider will usually change your official due date to match the scan. That's not a sign anything is wrong — it usually just means you ovulated earlier or later than assumed, or your LMP date was a little off. Once an early ultrasound sets the date, it generally sticks: later scans measure size, which varies a lot between perfectly healthy babies, so they aren't used to re-date the pregnancy.
Add 266 days — 38 weeks — to the day you conceived. So if you conceived on June 1, your estimated due date is February 22 of the following year. Keep in mind that even a known "conception date" has some wiggle room: sperm can survive up to five days, so fertilization may have happened a few days after the act itself. Choose the conception method above and the calculator does the math for you, including your gestational age today and the milestones ahead.
| Trimester | Weeks | What happens |
|---|---|---|
| First trimester | Weeks 1–13 | Major organs form, the heartbeat begins, and morning sickness and fatigue are common. Miscarriage risk drops sharply toward the end. |
| Second trimester | Weeks 14–27 | Often the most comfortable stretch. You’ll likely feel first kicks around weeks 18–22, and the anatomy scan happens around week 20. |
| Third trimester | Week 28 to birth | Baby gains weight fast and turns head-down. Appointments get more frequent, and your body starts preparing for labor. |
A due date calculator gives a solid estimate, but only about 4 to 5 percent of babies arrive on their exact due date. Most babies are born within a two-week window on either side. Your provider may fine-tune the date after a first-trimester ultrasound, which is the most accurate dating method.
Yes. If your first-trimester ultrasound measurement differs significantly from your LMP-based date, your provider will usually update your official due date to match the ultrasound. Once set by an early ultrasound, the due date typically is not changed again later in pregnancy.
Add 266 days (38 weeks) to your conception date. Pregnancy is usually counted as 40 weeks from the first day of your last period, but conception happens about two weeks after that, so the count from conception is 38 weeks.
IVF due dates are the most precise because the embryo’s age is known exactly. For a day-5 blastocyst transfer, add 261 days to the transfer date. For a day-3 embryo transfer, add 263 days.
The American College of Obstetricians and Gynecologists (ACOG) defines full term as 39 weeks 0 days through 40 weeks 6 days. Babies born at 37–38 weeks are called early term, and 41 weeks is late term.