Due Date Calculator

Your estimated due date, current week and trimester — from your last period.

FREE TOOL · WORKS OFFLINE · NO SIGN-UP

The LMP starts 20 weeks ago so you can see a sample result — change it to your own date.

Estimated due date
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Current week of pregnancy
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Progress so far
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Trimester
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Days until due date
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🤰 How to Use This Due Date Calculator

  1. 1.Enter the first day of your last period. Not the day it ended — the very first day it started. That is the date pregnancy weeks are counted from.
  2. 2.Check today's date. It is filled in for you, but you can change it to see your week on any past or future date.
  3. 3.Read your due date. The calculator adds 280 days (40 weeks) to your last period — the standard Naegele's rule used by doctors.
  4. 4.See your current week and trimester. Completed weeks plus days, the week you are in now, and which trimester that falls in.
  5. 5.Treat it as an estimate. Most babies arrive within about two weeks either side of the due date — an early ultrasound date from your doctor wins if they differ.

❓ FAQ

How is my due date calculated?

By Naegele's rule: 280 days (40 weeks) are added to the first day of your last period. It assumes a 28-day cycle with conception about two weeks after the period started. Only about 1 in 20 babies arrive exactly on the due date, so treat it as the middle of a likely window.

What week of pregnancy am I in?

Count the full weeks since the first day of your last period, not since conception. This tool shows both the completed weeks and days, and the week you are currently in — for example, 20 weeks and 3 days means you are in week 21.

What are the trimesters?

The first trimester runs through week 13, the second from week 14 to week 27, and the third from week 28 until birth. This calculator shows your current trimester automatically.

Can the due date change?

Yes — an early ultrasound can move it by a few days, especially if your cycles are irregular or longer or shorter than 28 days. Your doctor's date always wins; this tool gives the standard estimate.

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