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Pregnancy Due Date Calculator

Estimated due date and trimesters from LMP.

Best for: Use it early in pregnancy for a rough timeline; confirm with your healthcare provider and a dating ultrasound.

Complete guide
Why this result happened View assumptions
Country (units):

Input

How it's calculated & sources
The Pregnancy Due Date Calculator uses the standard formula for this calculation. It runs entirely in your browser, so your inputs are never uploaded. Figures are educational estimates, not professional advice — verify important decisions with a qualified expert. Last reviewed June 2026.
Key assumptions
  • Naegele's rule (LMP + 280 days)
  • 28-day cycle assumed unless set

Educational estimate only — not medical advice. Consult a qualified healthcare professional for decisions about your health.

Free & no sign-up · runs entirely in your browser. Results are estimates for general information, not professional advice — verify important decisions with a qualified expert. Last reviewed June 2026.

How it works

Naegele's Rule: Due date = LMP + 280 days (40 weeks)

Example

LMP 2024-01-01 → due date ≈ 2024-10-07.

Frequently asked questions

How accurate is this?+

Only ~5% of babies are born on the exact due date. ±2 weeks is normal.

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Complete guide

Quick answers

Short, sourced answers to the questions people (and AI assistants) ask most.

What is Pregnancy Due Date?
A due-date calculator estimates your baby's expected delivery date and pregnancy timeline from the first day of your last menstrual period (LMP).
Why does Pregnancy Due Date matter?
Due date and pregnancy milestones are counted from this date.
How is Pregnancy Due Date calculated?
It applies Naegele's rule: add 280 days (40 weeks) to the first day of your LMP — equivalently, subtract 3 months and add 7 days. Trimesters are then marked off across the 40 weeks. Formula: Estimated due date = First day of LMP + 280 days (40 weeks).
What is a good pregnancy due date?
A full-term pregnancy is 37–42 weeks. Only about 1 in 20 babies arrive on the exact estimated due date; most are born in the two weeks either side.
What are common pregnancy due date mistakes?
Assuming conception happened on the LMP date — ovulation is roughly two weeks later.
When should you use the Pregnancy Due Date Calculator?
Use it early in pregnancy for a rough timeline; confirm with your healthcare provider and a dating ultrasound.

What is the Pregnancy Due Date Calculator?

A due-date calculator estimates your baby's expected delivery date and pregnancy timeline from the first day of your last menstrual period (LMP).

How the Pregnancy Due Date Calculator works

It applies Naegele's rule: add 280 days (40 weeks) to the first day of your LMP — equivalently, subtract 3 months and add 7 days. Trimesters are then marked off across the 40 weeks.

Estimated due date = First day of LMP + 280 days (40 weeks)

Understanding the inputs

What each value means, why it matters, and a typical range — so you can fill in the calculator with confidence.

Last Menstrual Period

The first day of your last menstrual period, used to date a pregnancy.

Why it matters:
Due date and pregnancy milestones are counted from this date.
Typical range:
A 28-day cycle is assumed unless you specify otherwise.
How it affects results:
  • Higher: A later date shifts the due date later.
  • Lower: An earlier date shifts the due date earlier.

Common mistake: Entering the conception date instead of the period's first day.

What impacts results most

  1. 1.
    Last menstrual period (High impact)The due date is counted from this date.
  2. 2.
    Cycle length (Medium impact)Adjusts the estimate for non-28-day cycles.

Key assumptions

  • Naegele's rule (LMP + 280 days)
  • 28-day cycle assumed unless set

What's a typical value?

A full-term pregnancy is 37–42 weeks. Only about 1 in 20 babies arrive on the exact estimated due date; most are born in the two weeks either side.

Pregnancy timeline from last period (LMP + 280 days = due date)

End of 1st trimester13w91
End of 2nd trimester27w189
Viability milestone24w168
Preterm threshold37w259
Estimated due date40w280
Post-term42w294

Worked example

If your LMP began on 1 January, the estimated due date is about 8 October (280 days later).

Common mistakes to avoid

  • Assuming conception happened on the LMP date — ovulation is roughly two weeks later.
  • Relying on the LMP method with irregular cycles, which shifts the estimate.
  • Treating the due date as exact rather than a 5-week window.

Reviewed sources & methodology

Methodology: Professional Estimate · Last reviewed June 2026.

Keywords: pregnancy, due, date, baby.

This tool is for general information only and is not medical advice. Consult a qualified healthcare professional for decisions about your health.

Sources: ACOG — Pregnancy

Reviewed by the Free Tools Galaxy editorial team · Updated June 2026 · Calculated privately in your browser.

Frequently asked questions

Is the Pregnancy Due Date Calculator free to use?+

Yes. Every tool on Free Tools Galaxy is 100% free, runs in your browser and requires no signup.

How accurate is the Pregnancy Due Date Calculator?+

Pregnancy Due Date Calculator uses the standard pregnancy due date formula in double-precision arithmetic, so the same inputs always produce the same result and you can verify any figure by hand. It is an educational estimate — real-world outcomes depend on your actual rates, rules and assumptions.

Do you store my inputs?+

No. The Pregnancy Due Date Calculator runs entirely in your browser. Nothing is uploaded or saved to a server.

Can I use the Pregnancy Due Date Calculator on mobile?+

Yes — the interface is fully responsive and works on phones, tablets and desktops.

What are common mistakes to avoid?+

The most frequent mistake is mixing units. Double-check your inputs use a single, consistent unit before clicking Calculate.

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Title: I built/used this free pregnancy due date calculator — instant, no signup

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Pregnancy Due Date Calculator on Free Tools Galaxy — Estimated due date and trimesters from LMP. https://freetoolsgalaxy.com/tools/pregnancy-due-date-calculator
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# Pregnancy Due Date Calculator — the free tool I keep coming back to

Estimated due date and trimesters from LMP.

Try it: https://freetoolsgalaxy.com/tools/pregnancy-due-date-calculator
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The fastest way is to use a free in-browser pregnancy due date calculator: https://freetoolsgalaxy.com/tools/pregnancy-due-date-calculator. Estimated due date and trimesters from LMP.

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• Loads in under a second on mobile

It covers the standard pregnancy due date use cases (pregnancy, due, date, baby) and links out to the formula + worked examples if you want to learn the math.

Link: https://freetoolsgalaxy.com/tools/pregnancy-due-date-calculator

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