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Pregnancy Due Date Calculator
Find your estimated due date, current gestational age and trimester from your last menstrual period.
How due dates are calculated
Pregnancy is counted from the first day of your last menstrual period (LMP), not from the day of conception. That convention exists because most people know when their period started but not the exact moment they conceived. The standard estimate uses Naegele's rule: due date = LMP + 280 days (40 weeks). Conception itself usually happens about 14 days after the LMP, in the middle of an average cycle, which is why a typical pregnancy lasts roughly 38 weeks from conception but is reported as 40 weeks. This calculator adjusts for non-standard cycle lengths so the result remains accurate for shorter or longer cycles.
How to use this calculator
Pick the first day of your last menstrual period in the date picker. If your cycles are not 28 days, change the cycle length — for example a 32-day cycle pushes the due date 4 days later, since ovulation happens later in long cycles. The calculator instantly shows your estimated due date, your current gestational age in weeks and days, the trimester you are in, and the number of days remaining until your due date. Treat the result as an estimate: only about 4% of babies are born exactly on the due date.
How accurate is this estimate?
Naegele's rule assumes a 28-day cycle with ovulation on day 14. In reality both vary. A first-trimester ultrasound (typically between 8 and 12 weeks) is the most accurate dating method available — it can be off by only ±5 to 7 days. If your scan date and your LMP date disagree by more than a week, your provider will usually go with the ultrasound. Roughly 80% of babies are born within two weeks of the estimated due date; only about 4% on the exact day. A pregnancy past 41 weeks is considered "late term" and most providers recommend monitoring or induction by 42 weeks.
Trimesters at a glance
| Trimester | Weeks | Highlights |
|---|---|---|
| First trimester | 1 — 13 | Implantation, organ formation, first ultrasound, morning sickness peaks around week 9. |
| Second trimester | 14 — 27 | Belly shows, anatomy scan around week 20, first kicks felt by 18–22 weeks. |
| Third trimester | 28 — 40+ | Rapid growth, glucose test, group B strep test, baby positions for delivery. |
What to do once you have your due date
Knowing your estimated due date helps with three things: scheduling prenatal visits, planning maternity leave, and preparing for the baby's arrival. Most providers see you about every 4 weeks until 28 weeks, every 2 weeks from 28 to 36 weeks, and weekly from 36 weeks until birth. Common milestones tied to the due date include the first ultrasound (8–12 weeks), the anatomy scan (around 20 weeks), the glucose tolerance test (24–28 weeks), and the group B strep swab (35–37 weeks). Use the date as your anchor, mark these checkpoints in a calendar, and remember that any unusual bleeding, severe headaches, sudden swelling, or reduced fetal movement always warrants a same-day call to your provider — not a wait-and-see.