Pregnancy Due Date Calculator
100% private — runs on your device, never uploaded. Works offline once loaded.
Enter the first day of your last menstrual period, and optionally your average cycle length, to estimate your due date with Naegele's rule, along with how far along you are today and which trimester you are in. Everything is calculated on your device.
How the due date is estimated
This calculator uses Naegele's rule, the standard method for dating a pregnancy from the first day of the last menstrual period (LMP). The classic version adds 280 days — 40 weeks — to the LMP to give the estimated due date, because pregnancy is conventionally measured from the LMP rather than from conception, which typically occurs about two weeks later.
If your cycle is not the textbook 28 days, ovulation and conception shift accordingly, so the tool adjusts the estimate by the difference between your average cycle length and 28 days. A longer cycle pushes the due date slightly later, and a shorter cycle brings it earlier. The result is an estimated date, not a guarantee.
Gestational age and trimesters
Gestational age is how far along the pregnancy is, measured in completed weeks and days since the LMP. This calculator compares today's date with your LMP to show your current gestational age, then places you in a trimester based on standard boundaries.
The first trimester runs through week 13, the second from week 14 to week 27, and the third from week 28 until birth, with full term generally considered 37 to 42 weeks. Knowing your week helps you follow typical milestones and understand what antenatal appointments and screenings tend to fall when.
Because the calculation reads today's date each time you open it, your gestational age and countdown stay current without you re-entering anything.
What the estimate can and cannot tell you
A due date is a useful planning anchor, but it is genuinely an estimate. Studies consistently show that only around one in twenty babies arrives on the predicted day; the large majority are born within roughly two weeks before or after. An early ultrasound, especially in the first trimester, is often more accurate than LMP dating and may revise the date your clinician uses.
Treat this tool as a quick, private way to see your due date, current stage and countdown at a glance. It does not replace antenatal care, and any concerns about dates, symptoms or wellbeing should always be discussed with a midwife or doctor.
Frequently asked questions
What if I do not know my exact LMP?
The estimate depends on the LMP, so an uncertain start date makes it less reliable. In that case an early dating ultrasound is the best way to establish your due date and gestational age.
Why does cycle length change the result?
Naegele's rule assumes a 28-day cycle with ovulation around day 14. If your cycle is longer or shorter, conception shifts, so the tool adds or subtracts the difference to keep the estimate realistic.
Is the due date from conception or from my period?
From your last period. Pregnancy is conventionally dated from the first day of the LMP, which is about two weeks before conception, so 40 weeks from LMP is roughly 38 weeks from conception.
How are trimesters divided?
The first trimester covers up to week 13, the second spans weeks 14 to 27, and the third runs from week 28 to birth. Full term is generally considered 37 to 42 weeks.
Can this replace a doctor's estimate?
No. It is a convenient screening estimate. Clinicians confirm and often refine dating with ultrasound, and antenatal care should always guide medical decisions.
Is my information saved?
No. Your LMP date and cycle length are used only in your browser to compute the result, and nothing is uploaded or stored on a server.
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