Due Date Calculator
Enter the first day of your last period and we will estimate your due date, how many weeks pregnant you are now, and your trimester.
Due date questions
- How accurate is a due date calculator?
- It is an estimate based on a 280-day pregnancy counted from the first day of your last period. Only about 1 in 20 babies arrive on the exact due date, and most births happen in the two weeks on either side. An early dating ultrasound is more accurate, and your provider will confirm your date.
- How is the due date calculated?
- We use Naegele's rule: add 280 days, or 40 weeks, to the first day of your last menstrual period. If your average cycle is longer or shorter than 28 days, we shift the date by the difference so the estimate stays consistent with how far along you are.
- What if my cycle is not 28 days?
- Enter your average cycle length and the calculator adjusts. A longer cycle usually means you ovulated later, so the due date moves a little later, and a shorter cycle moves it earlier. If you are not sure, leave it at 28 and confirm with your provider.
- Can I use it if I do not know my last period?
- The calculator needs the first day of your last period. If you do not know it, or your cycles are irregular, an early dating ultrasound is the most reliable way to set a due date. Ask your provider at your first prenatal visit.