🤰 Pregnancy Due Date Calculator
Enter the first day of your last period (or your conception date) to find your estimated due date and exactly how many weeks and days pregnant you are.
Typical prenatal tests and milestones (follow your provider's schedule)
How to use the due date calculator
Choose what you know and enter the date — your gestational age and estimated due date appear instantly. Most people use the first day of their last menstrual period (LMP). If you know your ovulation or conception date, that can be more precise; if your doctor or midwife has already given you a due date (often adjusted after an early ultrasound), choose "I know my due date" to track your weeks from it. The table below converts the usual prenatal test windows into your own calendar dates.
How pregnancy weeks are counted
Pregnancy is dated from the first day of your last period, not from conception — that day is 0 weeks 0 days. Conception typically happens about two weeks later, which is why many people are already "4 or 5 weeks pregnant" when they get a positive test. "12w 3d" means 12 full weeks plus 3 days, i.e. you're in your 13th week.
How the due date is calculated (Naegele's rule)
- Due date
LMP + 280 days(40 weeks). By hand: add one year, subtract three months, add seven days. - Cycle adjustment Naegele's rule assumes a 28-day cycle. With a longer or shorter cycle the due date shifts by
(cycle − 28) days. - From conception
conception date + 266 days(conception is counted as 2w 0d). For IVF with a day-5 blastocyst transfer, the due date is the transfer date + 261 days; for a day-3 transfer, + 263 days. - Current week
(as-of date − LMP) ÷ 7— the quotient is weeks, the remainder is days.
Trimesters and term
| Stage | Weeks |
|---|---|
| First trimester | 0w 0d – 13w 6d |
| Second trimester | 14w 0d – 27w 6d |
| Third trimester | 28w 0d – birth |
| Early term | 37w 0d – 38w 6d |
| Full term | 39w 0d – 40w 6d |
| Late term | 41w 0d – 41w 6d |
| Post-term | 42w 0d and beyond |
Only about 1 in 20 babies arrives exactly on the due date; birth any time from 37 to 42 weeks is considered normal. An early ultrasound measuring the baby (crown-rump length) is the most accurate way to date a pregnancy, so if your provider has given you a due date, use it.
About the prenatal test table
The weeks shown are typical windows for common tests and scans in the US and many other countries. Exactly which tests you're offered — and when — depends on your provider, your age and health, and earlier results; some (like NIPT) are optional.
This is a date calculator, not a medical diagnosis. Always follow the dates and advice of your doctor or midwife. If you have bleeding, severe pain or other worrying symptoms, contact your provider right away.