The pregnancy due date calculator estimates your baby’s arrival date based on the first day of your last menstrual period (LMP) or your known conception date. It also tells you how many weeks pregnant you are today and your current trimester — all instantly, with no sign-up required.
How to Calculate Your Due Date
- Select your calculation method: Last Menstrual Period or Conception Date.
- Enter the relevant date.
- See your estimated due date, current week of pregnancy, and trimester.
How Due Dates Are Calculated
The standard method (Naegele’s Rule) adds 280 days (40 weeks) to the first day of your last menstrual period. This assumes a 28-day cycle with ovulation on day 14. Only about 5% of babies arrive on their exact due date — the normal delivery window is 38–42 weeks.
Frequently Asked Questions
How accurate is this due date estimate?
The LMP method is accurate to within 1–2 weeks for women with regular 28-day cycles. It becomes less accurate with irregular cycles or if you’re unsure of your LMP date. An early ultrasound (before 13 weeks) gives the most accurate due date and is used by most OBs to confirm or adjust the estimate.
What if my cycle is longer or shorter than 28 days?
If your cycle is consistently different from 28 days, your actual ovulation date shifts. For example, a 35-day cycle means ovulation around day 21 rather than day 14, pushing the due date about a week later. The calculator uses a standard 28-day cycle as the baseline.
What are the three trimesters?
The first trimester covers weeks 1–13, the second trimester weeks 14–26, and the third trimester weeks 27–40. Each has distinct developmental milestones and typical symptoms.
Can I use this for IVF pregnancies?
For IVF, use the conception/transfer date method rather than LMP, as the fertilization date is precisely known. Your fertility clinic will also provide an official due date based on your embryo transfer date.
What does “full term” mean?
Full term is defined as 39–40 weeks. “Early term” is 37–38 weeks, “late term” is 41 weeks, and “post-term” is 42+ weeks. Babies born before 37 weeks are considered preterm. Medical care and interventions vary based on these designations.