Example 1
- LMP: January 1, 2026
- Cycle length: 28 days
EDD = October 8, 2026
280 days from LMP gives October 8, 2026, with no cycle adjustment.
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.
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.
Result
Enter the first day of your last period.
How results are calculated
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.
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
- Type the first day of the last period, for example January 1, 2026.
- If the cycle is not 28 days, type that length beside it. An empty field keeps 28.
- Click Calculate. At 28 days the EDD is October 8, 2026. At 24 days it is October 4.
- The timeline under the form shows LMP, today, and that same date. At 35 days from January 1 it is October 15.
- This is 280 days from LMP plus a cycle tweak, not an ultrasound and not an IVF calendar.
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.
- EDD
- Estimated due date. A 35-day cycle from January 1, 2026 moves EDD to October 15, not the 8th.
Usage examples
Example 2
- LMP: January 1, 2026
- Cycle length: 24 days
EDD ≈ October 4, 2026
A cycle 4 days shorter comes out 4 days earlier than the classic 280.
Example 3
- LMP: January 1, 2026
- Cycle length: 35 days
EDD = October 15, 2026
Seven days past 28 gives an EDD of October 15, 2026 instead of October 8.
Example 4
- LMP: March 15, 2025
- Cycle length: 28 days
EDD = December 20, 2025
The same 280 days from March 15 gives a due date of December 20, 2025.
Example 5
- LMP: June 20, 2026
- Cycle length: 30 days
EDD ≈ March 29, 2027
Two days past 28 comes out as 282 days from LMP, due March 29, 2027.
Example 6
- LMP: February 14, 2026
- Cycle length: 21 days
EDD = November 14, 2026
Seven days below 28 gives 273 days from LMP and an EDD of November 14, 2026.
Example 7
- LMP: November 1, 2025
- Cycle length: 45 days
EDD ≈ August 25, 2026
Seventeen days past 28 comes out as 297 days from LMP, due August 25, 2026.
Example 8
- LMP: August 8, 2026
- Cycle length: 32 days
EDD = May 19, 2027
Four days past 28 gives 284 days from LMP and an EDD of May 19, 2027.
Related calculators
FAQ
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 jumpy cycle make this due date unreliable?
If cycle length jumps around, an average-cycle correction is only a rough sketch. 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.
Knowledge sources
Day counts and age follow the Gregorian calendar. This is date arithmetic, not a time-zone tool.
Page updated in 2026.