Pregnancy Due Date Calculator
Enter the first day of your last menstrual period to estimate your due date, how far along you are and the key dates in your pregnancy.
This is an estimate for planning, not medical advice. Only a healthcare provider can confirm your due date, usually with an ultrasound.
How to calculate your due date
- Enter the first day of your last menstrual period (the first day of bleeding, not the last).
- If your cycle is not 28 days long, change the average cycle length.
- Read your estimated due date, the current week and trimester, and the key dates ahead.
Features
Due date and week
See your estimated due date and how many weeks you are.
Key dates
Conception, trimesters, scan window and full term.
Cycle adjustment
Adjusts the due date for cycles shorter or longer than 28 days.
Private
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How your due date is estimated
Doctors usually count a pregnancy from the first day of your last menstrual period (LMP), not from conception. A full pregnancy is 40 weeks, or 280 days, from that date. This is Naegele's rule: add 280 days to the LMP, which is the same as adding one year, subtracting three months and adding seven days. Conception normally happens about two weeks after your period starts, so you are already "two weeks pregnant" on the day you ovulate.
The rule assumes a 28-day cycle with ovulation on day 14. If your cycle is longer or shorter, ovulation moves with it, so this calculator shifts the due date by the difference. For example, with a 32-day cycle the due date is four days later. Pregnancy is split into three trimesters: weeks 1 to 13, weeks 14 to 27 and week 28 until birth.
Only about 4 or 5 percent of babies arrive exactly on the estimated date, and a healthy birth can happen from week 37 to week 42. Your healthcare provider may change the date after an early ultrasound, which is more accurate if your cycles are irregular. This tool is for planning and curiosity, and is not medical advice.
Frequently asked questions
How is the due date calculated?
The due date is 280 days (40 weeks) after the first day of your last period, adjusted by the difference between your cycle length and 28 days.
What if my cycle is irregular or I am not sure of the date?
The estimate will be less reliable. Your doctor can date the pregnancy with an ultrasound, usually in the first trimester, which is more accurate.
How accurate is a due date?
Only about 5 percent of babies are born on the due date. Most are born within two weeks before or after it, and anything from 37 to 42 weeks is considered a normal birth time.
What are the three trimesters?
The first trimester is weeks 1 to 13, the second is weeks 14 to 27 and the third is week 28 until birth.
Is this medical advice?
No. It is a general estimate. Always follow the advice of your doctor or midwife, who can confirm your due date and care plan.