Estimate a pregnancy due date using either the first day of the last menstrual period or a known conception date.
Dating method
Choose a date to estimate from
Date estimate
Pregnancy date estimates
Estimated dates and timing
Your estimate will appear here
Choose a dating method and enter the corresponding date.
Estimated due dateLast-period method: date + 280 days, adjusted for cycle length; conception method: date + 266 days
Estimated due date
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Estimated pregnancy week
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Estimated trimester
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Time remaining
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This is a calendar estimate, not confirmation of pregnancy or an official obstetric due date. Clinical dating may differ; use guidance from your prenatal care professional, especially if an early ultrasound or assisted-reproduction dates are available.
What is Pregnancy Due Date?
The Pregnancy Due Date Calculator estimates a 40-week due date from either the first day of the last menstrual period or a known conception date. With the period method, it can make a simple adjustment for a usual cycle length from 21 to 35 days. It also shows estimated time remaining, the current pregnancy week and trimester.
This page is best used as a calendar explanation before or alongside prenatal care. It does not confirm pregnancy, assess fetal growth or decide the official obstetric date. Early ultrasound and known assisted-reproduction dates may provide better dating information than a recalled period.
How to Use This Calculator
Select “First day of my last period” when that date is known and reasonably reliable. Enter the first day, then choose the usual cycle length; use 28 or “I don’t know” when no dependable average is available.
Select “Date I conceived” only when there is a sound basis for that date. An intercourse date is not necessarily the date of fertilization.
Choose Calculate. The period method adds 280 days and adjusts by the difference between the chosen cycle and 28 days. The conception method adds 266 days.
Read the estimated due date and the calendar status calculated for today. A past due date produces zero remaining days, while the displayed current week is capped at week 40.
The form checks that the selected date is present and not in the future. It cannot check recall accuracy, cycle regularity or whether another clinical dating method should take priority.
Formula Used
Period method: EDD = first day of LMP + 280 days + (cycle length − 28 days). Conception method: EDD = conception date + 266 days. Estimated gestational age = today − LMP-equivalent date.
Variables Explained
Input or output
Meaning
Limitation
LMP
First day of the last menstrual period.
Recall, irregular bleeding or irregular cycles can reduce reliability.
Cycle length
Usual days from the first day of one period to the first day of the next.
A single average does not capture month-to-month variation.
Conception date
Date used as fertilization in the 266-day method.
It is often uncertain outside assisted reproduction.
EDD
Estimated calendar date at 40 weeks.
It is not a promised birth date.
Current week
Completed gestational weeks as of today.
This page caps the display at week 40.
Trimester
Broad stage based on the calculated current week.
It inherits any error in the starting date.
Worked Example
Take an LMP first day of 1 August 2026 and a usual cycle length of 30 days. The basic 280-day date is 8 May 2027. The cycle is two days longer than 28, so add two more days. The calculator returns an estimated due date of 10 May 2027.
The cycle adjustment assumes the later average cycle corresponds to later ovulation. That is a planning convention, not a measurement of ovulation in this particular cycle. An early ultrasound or treatment record can support a different clinical date.
Why Use This Calculator?
Use the date to understand how weeks are counted and to prepare questions for prenatal care. ACOG defines the first trimester through 13 weeks and 6 days, the second from 14 weeks through 27 weeks and 6 days, and the third from 28 weeks. The page assigns its text from completed weeks using those boundaries.
Time remaining changes each day and reaches zero when the estimate has passed. Zero does not say whether labor has begun or whether the pregnancy needs intervention. Likewise, a trimester label does not evaluate development, symptoms or pregnancy health.
A healthcare professional can compare menstrual history, ultrasound findings and any assisted-reproduction records, then document the best obstetric estimate. Contact a maternity service for questions about timing or symptoms. Severe pain, heavy bleeding, breathing difficulty, fainting or another emergency concern needs urgent assessment.
Common Mistakes
Using the last day of bleeding instead of the first.
Choosing the longest or shortest cycle ever observed rather than a usual length.
Assuming the date of intercourse is certainly the conception date.
Reading “weeks remaining” as a countdown that guarantees delivery on zero.
Using the calculation to confirm pregnancy or judge whether fetal growth is normal.
Ignoring an early ultrasound or assisted-reproduction record that a clinician uses for dating.
Changing a documented due date without discussing the evidence with the maternity team.
Frequently Asked Questions
Why are 280 days added to the last period?
Gestational age is conventionally counted from the first day of the last menstrual period. Forty weeks equals 280 days and includes roughly two weeks before conception in a textbook 28-day cycle.
What should I enter if I do not know my cycle length?
Select the 28-day default marked “I don’t know.” Recognize that an uncertain or irregular cycle makes this menstrual estimate less dependable.
Why does cycle length change the result?
The simple adjustment assumes ovulation shifts by the same number of days that the usual cycle differs from 28 days. Individual cycles may not follow that assumption.
Is a conception-date estimate always more accurate?
Only when conception is genuinely known. A remembered intercourse date may differ from fertilization, while assisted-reproduction records can provide much firmer timing.
What happens after the calculated due date passes?
The page shows zero days remaining and caps the current week at 40. That display is arithmetic only; contact the maternity team for personal guidance.
Can this result replace an ultrasound date?
No. ACOG identifies first-trimester ultrasound as the most accurate method to establish or confirm gestational age, and clinical dating may revise an LMP estimate.
Does the trimester label show that the pregnancy is healthy?
No. It groups elapsed gestational time. It does not assess symptoms, fetal growth, test results or wellbeing.