Pregnancy Due Date Calculator
Wondering when your baby is due, or how far along you are? This free calculator estimates your due date, gestational age in weeks and days, trimester and baby length — privately, with nothing uploaded.
What is a pregnancy due date calculator?
A pregnancy due date calculator estimates when your baby will be born and how far along you are, from a single reference date. The most common method is Naegele's rule: take the first day of your last menstrual period (LMP) and add 280 days (40 weeks).
This free calculator takes that LMP date plus your average cycle length and returns your estimated due date, your gestational age in weeks and days, your trimester and an approximate baby length. You can also switch to the conception-date method, which adds 266 days from the day you confirm conception.
Remember, the result is an estimate: babies rarely arrive on the exact date, and it should never replace professional medical care.
How to use this due date calculator
- Pick whether to calculate from your last period or your conception date.
- Enter the first day of your last menstrual period (or your conception date).
- Set your average cycle length — 28 days is the typical default.
- Click Calculate Due Date to see the estimate, your weeks and days, trimester and baby length.
How the due date is calculated
Due date = LMP date + 280 days (40 weeks); gestational age days = today − LMP; trimester split: 1st 0-13wk, 2nd 14-27wk, 3rd 28wk+
Naegele's rule assumes a 28-day cycle with ovulation near day 14, so it adds 280 days to the last period. A longer or shorter cycle shifts the date, and gestational age is the completed weeks and days between the LMP and today.
Example
If your last menstrual period started on January 15, 2026, the estimated due date is October 22, 2026 (LMP + 280 days). Checking on June 1, 2026 your gestational age would be 19 weeks 4 days (137 days), which puts you in the second trimester (14-27 weeks). These are the exact figures this calculator returns using the LMP method with a 28-day cycle.
Common use cases
- Answering "how far along am I": get your current weeks and days in an instant.
- Planning the due date: estimate the arrival window for leave, travel and preparations.
- Tracking the trimester: know when you enter the second and third trimesters.
- Comparing methods: compare a last-period estimate with a conception-date estimate.
Pro tips
- Stick to one reference date: the LMP is what most clinics use, so it keeps your figures comparable.
- Adjust the cycle length: with irregular or longer cycles, the default 28 days may shift the estimate.
- Plan around a two-week window: only about 5% of babies arrive exactly on the due date.
- Confirm with a dating scan: an ultrasound near 8-14 weeks is the most accurate estimate.
Pregnancy Due Date Calculator FAQ
How is my pregnancy due date calculated?
It is estimated with Naegele's rule: take the first day of your last menstrual period (LMP) and add 280 days, which is 40 weeks.
How accurate is a due date?
Only about 5% of babies arrive exactly on the due date. Most are born within a two-week window either side, so treat it as an estimate.
How far along am I in weeks?
Gestational age is the number of completed weeks and days since your last menstrual period, shown for the date you check.
How long is a full-term pregnancy?
A full-term pregnancy is about 40 weeks (280 days) from the last menstrual period. The term range runs from 37 to 42 weeks.
When do I enter my second and third trimesters?
The first trimester runs from week 0 to 13, the second from week 14 to 27, and the third from week 28 to the birth.
What is the difference between gestational and fetal age?
Gestational age counts from the last period; fetal (or fertilization) age is about two weeks less, counting from conception.
Does my cycle length change the due date?
Yes. A longer cycle delays ovulation and shifts the due date later, which is why you can enter your cycle length here.
What is the difference between the LMP and conception methods?
The LMP method adds 280 days to the last period; the conception method adds 266 days to the known date of conception.
Why is my ultrasound due date different?
An ultrasound dates the pregnancy by measuring the fetus, so it can fall a little earlier or later than the period-based estimate.
Is this a medical pregnancy calculator?
No. It is an educational estimate. For a personalized or high-risk pregnancy, confirm your dates with your doctor or midwife.
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