Pregnancy Calculator

Find your estimated due date in seconds with this free pregnancy due date calculator. Enter the first day of your last menstrual period (LMP), or work backwards from a due date you already have. You will see the estimated due date, how many weeks pregnant you are today, and which trimester you are in. Everything runs in your browser, so your dates never leave your device.

Pregnancy Due Date Calculator

LMP means the first day of your last period before pregnancy. Pick the date from the calendar.

Estimate only — not medical advice. Your healthcare professional's dating, especially ultrasound dating, takes precedence. Talk to a healthcare professional about personal decisions. All calculations run in your browser; nothing is sent or stored.

How the due date is worked out

Doctors count pregnancy as 40 weeks, or 280 days, from the first day of the last menstrual period. This is called Naegele’s rule. It assumes a regular 28-day cycle with ovulation around day 14, which is why the due date is an estimate and not a promise.

From LMP: estimated due date = LMP + 280 days.

From a due date: estimated LMP = due date − 280 days.

Gestational age today: (today − LMP) in days, shown as weeks and days. Trimester: weeks 1–13 is the first trimester, weeks 14–27 is the second, and week 28 onwards is the third.

Solved example: LMP 1 January 2026

Take an LMP of 1 January 2026 and work through the steps.

Step 1: Start with the LMP: 1 January 2026.
Step 2: Add 280 days (40 weeks): 1 January 2026 + 280 days = 8 October 2026.
Step 3: The estimated due date is 8 October 2026.
Step 4: On 1 November 2026, gestational age is (1 November − 1 January) = 304 days = 43 weeks and 3 days, which is the third trimester.

How to use this calculator

  • Choose whether to start from your LMP date or from a due date you already have.
  • Pick the date from the calendar. LMP means the first day of your last period before this pregnancy.
  • Press Calculate and read your estimated due date, current week and day count, and trimester.

Limits: due dates are estimates, not medical advice

The due date from this calculator is an estimate only. It is not medical advice, and it does not diagnose anything or replace care from a healthcare professional.

Only about 1 in 20 babies arrives exactly on the due date. Cycles vary in length, ovulation does not always happen on day 14, and the LMP date can be misremembered. A healthcare professional’s dating takes precedence over this estimate, especially ultrasound dating in early pregnancy, which measures the baby directly.

Do not use this result to make medical decisions on your own, such as changing medication or planning a delivery date. Talk to a midwife, doctor, or other healthcare professional about anything that affects you or your pregnancy. All calculations run in your browser. Nothing you enter is sent, stored, or logged, and the page never asks for your name, email, or account.

Frequently asked questions

What does LMP mean in this pregnancy due date calculator?

LMP stands for last menstrual period. It means the first day of bleeding of your last period before you became pregnant. Doctors use it as the starting point for dating a pregnancy because ovulation day is often unknown, while the LMP date is easier to remember or look up.

Why is the due date 40 weeks from the LMP?

It is a convention called Naegele’s rule. It assumes conception happens about two weeks after the LMP, so the 40 weeks include roughly two weeks before conception. That is why gestational age is usually about two weeks more than the age of the embryo itself.

Can I use this calculator if my cycles are irregular?

You can, but treat the result with extra caution. The 280-day rule assumes a regular 28-day cycle. With irregular cycles, ovulation may happen earlier or later than day 14, so the LMP-based date can be off by a week or more. An early ultrasound gives a more reliable date in that case.

What if my ultrasound date differs from this estimate?

Trust the ultrasound dating from your healthcare professional. Early ultrasound measures the baby directly and is more accurate than counting from the LMP, especially when cycles are irregular or the LMP date is uncertain. This calculator is a quick estimate; your clinician’s dating takes precedence.

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