Due date calculator

We compute EDD with Naegele's rule: first day of the last period (LMP) plus 280 days, adjusted if the cycle is not 28 days. A 28-day cycle from January 1, 2026 is October 8, 2026. A 24-day cycle gives October 4, a 35-day cycle gives October 15. That is obstetrics' starting point, not a sure birth day.

Input data

First day of last period (LMP)

Typical cycle length

Optional: 21 to 45 days (default 28). Leave blank for 28. The buttons set the same value as the field beside them.

Abbreviations

  • LMP (last menstrual period): first day of bleeding of your last period before pregnancy; the reference used in this field and in international clinical texts.
  • EDD (estimated due date): the estimated delivery date, exactly what the result shows.
  • C: typical cycle length in days. In the formula EDD = LMP + 280 + (C − 28).

Educational ballpark tool. Not a substitute for medical advice or a dating ultrasound.

Result

Enter the first day of your last period.

We compute EDD with Naegele's rule: LMP plus 280 days, adjusted if the cycle is not 28 days. January 1, 2026 and 28 days give October 8, 2026. Birth often lands about two weeks before or after that date. Confirm with your doctor, especially with irregular cycles.

How results are calculated

From January 1, 2026 on a 28-day cycle EDD = October 8, 2026
LMPJan 1, 2026
Days280
EDDOct 8, 2026

Naegele's rule. EDD is the first day of your last period (LMP) plus 280 days, or 40 weeks. The model assumes a 28-day cycle and ovulation around day 14. Pregnancy weeks on charts also start from LMP, not conception, so early pregnancy looks about two weeks ahead of fertilization. That is obstetric convention, not a dating error.

Cycle adjustment. If your typical cycle has C days, we compute EDD = LMP + (280 + (C minus 28)). A 24-day cycle gives 276 days from LMP; a 35-day cycle gives 287. An empty cycle field is treated as 28. Input is limited to 21 to 45 days, because outside that range an average length is a poor stand-in for ovulation day.

How to read the result. The date is an estimated EDD, not the day the baby must arrive. Many births fall in a window of about two weeks around that date.

An early ultrasound often overrides the LMP date when embryo size does not match the period calendar. The week number next to the date is only full weeks from LMP to today, when today sits between LMP and EDD.

What is not here. This model does not date a pregnancy after IVF, embryo transfer, or insemination. Those start from the procedure day, not LMP.

We do not draw a week-by-week calendar or a baby size chart. The tool is educational: a first answer to when is my due date, and a way to prepare for a visit, not a substitute for your clinician.

Calendar mnemonic. The classic Naegele form is also: from LMP subtract 3 months, add 7 days and 1 year. From January 1, 2026 that lands on October 8, 2026 — the same result as LMP + 280 days on a 28-day cycle. When the cycle has C days, first compute 280 + (C − 28), then the date.

Clinical backbone. ACOG's committee opinion on methods for estimating the due date treats 280 days from LMP as the starting point, and early ultrasound as the tool that can revise that date when embryo size does not match the period calendar. This calculator shows only the LMP + cycle-adjustment layer.

What this calculator shows

  • an estimated due date from LMP and cycle length using Naegele's rule,
  • how many days from the period go into the date after the cycle correction,
  • an approximate pregnancy week today if the LMP date is already in the past,
  • a timeline under the form with LMP, today's point, and the EDD.

What this model does not count

  • it does not replace a dating ultrasound or your clinician's call,
  • it does not date a pregnancy from IVF, embryo transfer, or insemination,
  • it does not build a week-by-week calendar or a baby size chart,
  • it does not promise a birth day, only an LMP-based EDD estimate.

How to use

  1. Enter the first day of the last period, for example January 1, 2026.
  2. If the cycle is not 28 days, enter that length beside it. An empty field keeps 28.
  3. Click Calculate. At 28 days the EDD is October 8, 2026. At 24 days it is October 4.
  4. The timeline under the form shows LMP, today, and that same date. At 35 days from January 1 it is October 15.
  5. This is 280 days from LMP plus a cycle tweak, not an ultrasound and not an IVF calendar.

Formula

EDD = LMP + 280 + (C − 28)

LMP — first day of the last period; C — typical cycle length in days (default 28); 280 days = 40 weeks.

That is Naegele's rule (Franz Karl Naegele, 19th century) — the classic obstetric starting point. ACOG treats 280 days from LMP as the baseline that early ultrasound can revise. On a 28-day cycle from January 1, 2026: EDD = October 8, 2026; at 24 days: October 4.

Equivalent calendar mnemonic: from LMP subtract 3 months, add 7 days and 1 year (on a 28-day cycle).

Naegele, LMP, and EDD

EDD = LMP + 280 + (cycle minus 28). From January 1, 2026 at 28 days that is October 8, 2026. At 24 days: October 4.

Naegele
The 280-day rule from LMP on a 28-day cycle. January 1, 2026 gives EDD October 8, 2026.
LMP
First day of the last period. That is the start field, not the conception day. From March 15, 2025 the EDD is December 20, 2025.
C
Typical cycle length in days. In the formula the correction is C minus 28; a 35-day cycle adds 7 days to 280.
EDD
Estimated due date. A 35-day cycle from January 1, 2026 moves EDD to October 15, not the 8th.

Usage examples

Example 1

  • LMP: January 1, 2026
  • Cycle length: 28 days

EDD = October 8, 2026

What due date for LMP January 1, 2026 and a 28-day cycle? October 8, 2026 (280 days).

Example 2

  • LMP: January 1, 2026
  • Cycle length: 24 days

EDD ≈ October 4, 2026

What EDD for LMP January 1, 2026 and a 24-day cycle? About October 4, 2026 — 4 days earlier than a 28-day cycle.

Example 3

  • LMP: January 1, 2026
  • Cycle length: 35 days

EDD = October 15, 2026

What EDD for LMP January 1, 2026 and a 35-day cycle? October 15, 2026 instead of October 8.

Example 4

  • LMP: March 15, 2025
  • Cycle length: 28 days

EDD = December 20, 2025

What EDD for LMP March 15, 2025 and a 28-day cycle? December 20, 2025 (280 days).

Example 5

  • LMP: June 20, 2026
  • Cycle length: 30 days

EDD ≈ March 29, 2027

What EDD for a 30-day cycle from that LMP? March 29, 2027 (282 days from LMP).

Example 6

  • LMP: February 14, 2026
  • Cycle length: 21 days

EDD = November 14, 2026

What EDD for a 21-day cycle? November 14, 2026 (273 days from LMP).

Example 7

  • LMP: November 1, 2025
  • Cycle length: 45 days

EDD ≈ August 25, 2026

What EDD for a 45-day cycle? About August 25, 2026 (297 days from LMP).

Example 8

  • LMP: August 8, 2026
  • Cycle length: 32 days

EDD = May 19, 2027

What EDD for a 32-day cycle? May 19, 2027 (284 days from LMP).

Related calculators

Ovulation and fertile window

Ovulation calculator: the first day of your last period and cycle length.

Use calculator →

Pregnancy weight gain

Pregnancy weight gain calculator: pre-pregnancy BMI or mass and height, plus the week.

Use calculator →

BMI (body mass index)

BMI calculator: weight and height.

Use calculator →

All date and time calculators

FAQ

How do I calculate a due date from the last period?

Add 280 days to the first day of the last menstrual period (Naegele’s rule). With a 28-day cycle from January 1, 2026, EDD is October 8, 2026.

How many weeks is pregnancy in this method?

280 days is conventionally 40 weeks from LMP. The calculator shows an EDD; it does not replace ultrasound dating or clinical judgment.

Is this the same as a pregnancy week tracker?

Here the result is an estimated due date from LMP and cycle length. Week-of-pregnancy tools show progress today — this card computes EDD.

Is this a free due date calculator?

Yes. Enter LMP and cycle length — the result shows at once, with no account.

Where do the 280 days in a due date come from?

Classic Naegele's rule adds 280 days, or 40 weeks, from LMP. On a 28-day cycle from January 1, 2026 the EDD is October 8, 2026, not an ultrasound date.

How does cycle length move the estimated due date?

The correction is the difference from 28 days added to 280. A 24-day cycle from January 1, 2026 gives October 4, and a 35-day cycle gives October 15.

Does birth happen exactly on the calculated day?

Rarely on the exact EDD. October 8, 2026 from January 1 is an estimate, and most births fall about two weeks before or after that date.

How is Due date calculator different from Ovulation and fertile window?

LMP is the first day of bleeding, and conception in a 28-day cycle is usually about two weeks later. That is why EDD October 8, 2026 is counted from January 1, not from the conception day.

What does EDD mean next to the result?

EDD means estimated due date. With LMP January 1, 2026 and a 28-day cycle we show October 8, 2026 so you can plan visits, not as a guarantee of the day labor starts.

Does this result replace a dating ultrasound?

No. An early ultrasound often dates the pregnancy more precisely and can override the LMP date. October 8, 2026 from January 1 is a quick start before your visit, not a diagnosis.

Does Naegele's rule work after IVF or embryo transfer?

No. After IVF or embryo transfer, dating starts from the transfer or retrieval day, not from LMP. This page only runs Naegele: 280 days from the period, such as October 8 from January 1, 2026.

Does a highly irregular cycle make this due date unreliable?

If cycle length varies a lot, an average-cycle correction is only a rough estimate. A 35-day cycle moves January 1, 2026 to October 15, but a clinician and ultrasound give a more reliable age than LMP alone.

Is the week next to the date a full pregnancy calendar?

No. Next to the EDD we only show how many full weeks have passed from LMP to today. From January 1, 2026 to October 8 we do not draw a week-by-week calendar or a baby size chart.

How should I quote this date with my doctor?

Say it is an estimate from LMP and your cycle length, without ultrasound. For January 1, 2026 and 28 days that is October 8, 2026, and your clinician will compare it with the exam and set the chart date.

· Hubert Ligocki

From LMP January 1, 2026 on a 28-day cycle the EDD is October 8, 2026. That is Naegele's rule, not an ultrasound.

Knowledge sources

The model is Naegele's rule: 280 days (40 weeks) from LMP on a 28-day cycle, plus the C − 28 correction. Day counts follow the Gregorian calendar.

Page updated in 2026.