Due Date & Pregnancy Calculator
This pregnancy calculator estimates your due date from the first day of your last menstrual period (LMP). Enter that date and your average cycle length and it instantly returns the estimated day your baby is due, how many weeks and days pregnant you are right now, which trimester you are in, and the approximate date of conception. It is a quick way to plan appointments, track milestones, and follow your pregnancy week by week.
Estimated due date
Current gestational age
Trimester
Estimated conception date
This is only an estimate based on Naegele’s rule and a regular cycle. The actual delivery date may vary; always consult a healthcare professional for proper pregnancy care.
Publicidad
How it works
The due date is estimated with Naegele’s rule: 280 days (40 weeks) are added to the first day of your last menstrual period, because pregnancy is dated from the LMP rather than from conception. If your cycle is longer or shorter than the standard 28 days, the estimate is shifted by the difference, since ovulation, and therefore conception, happens correspondingly later or earlier. Conception is placed about 14 days before your next expected period. Your current gestational age is simply the number of days that have passed since your LMP, expressed in completed weeks and days.
Naegele’s rule with a worked example
Naegele’s rule, published in the early 19th century, is still the standard way to date a pregnancy. The quick version is: take the first day of your last period, subtract 3 months, then add 7 days (and a year). Say your last period started on 10 January 2026: going back three months lands on 10 October 2025, and adding 7 days gives an estimated due date of 17 October 2026 — exactly 280 days later. It assumes a regular 28-day cycle with ovulation on day 14, which is why this calculator shifts the result when you enter a different cycle length. Keep in mind it is only an estimate: roughly 1 in 20 babies (about 5%) actually arrives on the predicted day, and an early dating ultrasound between weeks 8 and 13 is more accurate and may move the date by a few days.
The three trimesters at a glance
Pregnancy is counted from the last period and divided into three trimesters. The table sums up the week ranges and some general milestones for each stage; every pregnancy is different, so treat them as a rough map rather than a schedule.
| Trimester | Weeks | General milestones |
|---|---|---|
| First | 1–13 | Major organs and neural tube form, heartbeat becomes detectable, morning sickness is common |
| Second | 14–27 | First movements are felt, sex may be seen on ultrasound, the bump grows and energy often returns |
| Third | 28–40 | Rapid weight gain, the lungs mature, the baby usually settles head-down ready for birth |
Publicidad
Preguntas frecuentes
- How is my due date calculated?
- The most common method, Naegele’s rule, adds 280 days (40 weeks) to the first day of your last menstrual period. Pregnancy is dated from the LMP because it is easier to identify than the exact day of conception. This calculator also adjusts the estimate when your cycle differs from the typical 28 days.
- What is the LMP (last menstrual period)?
- The LMP is the first day of bleeding of your most recent period, before you became pregnant. It is the standard starting point for dating a pregnancy and calculating both your due date and your current gestational age in weeks.
- How accurate is the estimated due date?
- Only about 4 in 100 babies are born exactly on their due date. Most arrive within two weeks before or after it. The estimate is most reliable when your cycles are regular; an early ultrasound gives a more precise date and is what doctors ultimately rely on.
- How are the three trimesters divided?
- Pregnancy is split into three trimesters by gestational week: the first trimester runs through week 13, the second from weeks 14 to 27, and the third from week 28 until birth. This calculator shows which trimester your current gestational age falls into.
- Why does cycle length change the result?
- The standard rule assumes a 28-day cycle with ovulation on day 14. If your cycle is longer, you ovulate and conceive later, so your due date moves later by the same number of days; a shorter cycle moves it earlier. Adjusting the cycle length makes the estimate more personal.