IndCalc
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Estimate your due date, current pregnancy week, trimester progress, and upcoming milestones. Choose between LMP, conception date, or ultrasound dating with cycle-length adjustment.
Knowing your due date helps plan prenatal visits, antenatal classes, maternity leave, and key screenings such as the NT scan and anomaly scan. The result is an estimate — natural birth typically occurs anywhere between 37 and 42 weeks.
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The most common way to estimate a pregnancy due date is Naegele's rule, which adds 280 days (40 weeks) to the first day of the last menstrual period (LMP). This assumes a regular 28-day cycle with ovulation around day 14.
If your cycle is longer or shorter than 28 days, the due date shifts accordingly because ovulation happens later or earlier within the cycle. This calculator adjusts for cycle length automatically when you choose the LMP method.
When the conception date is known precisely (for example after IVF or careful tracking), counting forward 266 days gives a more direct estimate. Ultrasound dating in the first trimester is considered the most accurate medical method and is what doctors rely on if LMP and ultrasound disagree.
The first trimester runs from week 1 to week 12 and includes the highest sensitivity to medication and the highest natural miscarriage risk. The NT (Nuchal Translucency) scan window typically falls between weeks 11 and 13.
The second trimester (weeks 13 to 26) usually brings reduced nausea and the anatomy or anomaly scan around weeks 18 to 22, when many parents learn the baby's sex. Movements (quickening) often start being felt between weeks 18 and 22.
The third trimester (weeks 27 to 40) is the growth phase. Babies are considered full-term from week 37, and most arrive between week 38 and week 42. Only around 5% of babies are born on the calculated due date itself.
Use LMP dating if you have regular cycles and remember the first day of your last period. It is the standard method used by most clinicians for an initial estimate. The cycle-length adjustment improves accuracy if your cycle is not 28 days.
Use conception date if you tracked ovulation precisely or had assisted reproduction such as IUI or IVF. This is the most direct way to count, and it matches embryology more closely.
Use ultrasound dating if you have already had a first-trimester scan. Early ultrasound CRL (crown-rump length) measurement is highly accurate, and most modern obstetric guidelines recommend updating the due date when ultrasound and LMP differ by more than 5 to 7 days.