✦Introduction
Introduction
This pregnancy due date calculator provides an estimated date for delivery from the first day of the last menstrual period or, when available, a known conception date. It is a planning estimate rather than a promise of the exact day a baby will be born.
Pregnancy timing varies between people and pregnancies. Use the result as a conversation aid with a qualified clinician, and follow your care team when an ultrasound or clinical assessment provides a different estimate.
％Definition
What is an estimated due date?
An estimated due date is a calendar date about 40 weeks from the first day of the last menstrual period in a typical 28-day cycle. The calculation conventionally counts 280 days, although normal births can occur before or after that date.
If conception timing is known, the estimate is commonly based on about 38 weeks from conception. Ovulation and cycle length can shift the result, so the date should be treated as an estimate and updated by a clinician when appropriate.
↗How to use
How to use this calculator
- Choose whether you know the first day of your last menstrual period or a conception date.
- Enter the date using the calendar and confirm the displayed month, day, and year.
- If your cycle is regularly longer or shorter than 28 days, enter the cycle-length adjustment when the calculator provides that option.
- Review the estimated due date, estimated conception window, and trimester milestones as planning information.
- Take the result to a qualified healthcare professional, especially if your dates are uncertain or symptoms require urgent care.
Example 01LMP at the start of JanuaryWhat is the estimate when the last menstrual period began on January 5?
Example 02Known conception dateWhat happens when conception was estimated on March 12?
Example 03Longer cycleHow can a 32-day cycle affect the estimate?
Example 04Shorter cycleHow can a 25-day cycle affect the estimate?
Example 05Uncertain period dateWhat if the first day of the last period is not certain?
Example 06Ultrasound differsWhat if an ultrasound provides a different gestational estimate?
◎Result interpretation
How to interpret the result
The result is an estimated due date, not a scheduled delivery date. Only a small proportion of babies are born on the exact estimated date.
The estimated date can help organize appointments and prepare questions, but it cannot predict labor, identify complications, or establish that a pregnancy is progressing normally.
!Common mistakes
Common mistakes
Entering the last day rather than the first day of the last menstrual period.
Confusing the date of intercourse with a confirmed conception date.
Ignoring an unusually long or short cycle when interpreting a calendar estimate.
Treating the result as a diagnosis or delaying urgent medical care because of the calculated date.
◇Limits and special cases
Limitations and safety
This tool cannot confirm pregnancy, detect ectopic pregnancy, assess fetal growth, diagnose miscarriage, or replace prenatal care.
Seek urgent medical help for severe pain, heavy bleeding, fainting, difficulty breathing, or any symptom that concerns you. Contact a healthcare professional for personalized dating and care advice.
؟Frequently asked questions
FAQ
How accurate is a due date calculator?
It is a calendar estimate. Accuracy depends on the reliability of the entered date, cycle regularity, ovulation timing, and clinical assessment.
Why are 40 weeks counted from the last period?
The convention counts from the first day of the last menstrual period, which is usually earlier than conception by about two weeks.
Can the due date change?
Yes. A clinician may revise dating after reviewing cycle history, examination, or an ultrasound, particularly when the original date is uncertain.
What if I do not know my last menstrual period?
Use a known conception estimate if available, or ask a healthcare professional about the best way to establish gestational dating.
Does a longer cycle change the result?
It can. A cycle-length adjustment may move the estimate later or earlier than the standard 28-day-cycle calculation.
Does this calculator tell me the baby’s sex?
No. A due date calculation provides timing information and cannot determine fetal sex.
Can I use this for twins or multiples?
Use it only as a rough calendar reference and discuss care and timing with a clinician, because multiple pregnancies require individualized assessment.
When should I contact a clinician?
Contact a qualified clinician for prenatal guidance, uncertain dates, concerning symptoms, or any question about your health or pregnancy.
