Due Date Calculator

The estimated due date helps locate pregnancy in time, follow gestational weeks, trimesters and key prenatal milestones. It remains an estimate to confirm with the professional following the pregnancy.

Formula used

EDD = LMP + 280 days + cycle adjustment; or conception date + 266 days

The most common method adds about 280 days to the first day of the last menstrual period, with adjustment if the cycle is not 28 days. A known conception date can use 266 days, and ultrasound dating can recalculate an estimated start date.

Worked example and result reading

Situation

Example: if the first day of the last period is 8 May 2024 and the cycle is 28 days, the estimated due date is about 12 February 2025.

Interpretation

The displayed date helps organize follow-up, understand progress and prepare for birth. It does not guarantee the actual birth day, as many births happen before or after the estimate.

Detailed calculation guide

How should you use the calculator?

Enter the first day of the last period, average cycle length, or use conception date or ultrasound dating if those details are more reliable.

Why use the last period?

Gestational dating starts from the first day of the last period. It is a simple way to locate pregnancy from the start.

Why does cycle length change the date?

A longer cycle may mean later ovulation. A shorter cycle may bring the estimated date closer.

How do you read weeks?

Gestational weeks start from the last period. Pregnancy weeks start closer to conception, often about two weeks later.

Why show key milestones?

Landmarks such as 12 weeks, 22 weeks, 37 weeks or 40 weeks help understand progress without replacing a personalized medical calendar.

When should you be cautious?

Irregular cycles, uncertain LMP, assisted reproduction, multiple pregnancy, symptoms or different ultrasound dating should be discussed with a health professional.

Key takeaways

The due date is a benchmark, not a guarantee.
The LMP method uses the first day of the last period.
Cycle length can move the estimate earlier or later.
Ultrasound and medical follow-up can refine or change dating.

Decision checklist

Enter the first day of the last period, not the last.
Enter a realistic cycle length.
Use conception only when the date is reliable.
Read gestational and pregnancy weeks separately.
Keep uncertainty visible.
Confirm dating with medical follow-up.

Result checks before use

Read the result as a marker

A health or wellness calculator gives an order of magnitude based on general formulas. It does not replace diagnosis, medical follow-up or individual assessment, especially during pregnancy, illness, treatment or unusual symptoms. Use the number as preparation for a better-informed discussion, not as a standalone verdict.

Check personal inputs

Age, height, weight, sex, activity, cycle data or heart rate should be entered carefully. A simple input error can strongly change interpretation for energy needs, heart-rate zones or body markers.

Watch the trend

Use the result to follow a trend rather than judge a single day. Sleep, hydration, activity and energy expenditure naturally vary; a consistent average is more useful than a conclusion from one calculation. Recheck the inputs when your routine, weight, training or objective changes.

Get advice when needed

If the result affects an important medical, nutrition or training decision, confirm it with a qualified professional. Personal context, history and goals can completely change the correct interpretation.

Key pregnancy milestone table

These landmarks help locate progress, but real appointments depend on medical follow-up, country and pregnancy profile.

Milestone	Indicative period	Reading
12 weeks	End of first trimester	First major follow-up landmark
22 weeks	Middle of second trimester	Morphology follow-up period
28 weeks	Start of final part	Progressive preparation
32 weeks	Advanced third trimester	Closer follow-up depending on profile
37 weeks	Term window	Birth possible within the term period
40 weeks	Estimated term	Reference calculated date
41–42 weeks	After term depending on context	Possible strengthened medical follow-up

Scenarios to compare

Standard LMP

An LMP on 8 May 2024 and a 28-day cycle gives an estimated date around 12 February 2025.

Long cycle

A 31-day cycle adds about 3 days to the standard estimate.

Known conception

A known conception date can be completed with 266 days to estimate a due date.

Ultrasound

An ultrasound measurement can recalculate an estimated start date when LMP is uncertain.

Term window

The estimate should be read with a term window, not as an exact appointment.

Common mistakes to avoid

Confusing estimated date with guaranteed date.
Entering the last day of the period.
Forgetting cycle length.
Confusing gestational weeks and pregnancy weeks.
Ignoring reliable ultrasound dating.
Using the calculator as medical advice.

What to know before using the result

Due Date Calculator is an educational tool. It does not replace medical advice, diagnosis or personalized care, especially for children, pregnancy, athletes or specific clinical situations.

Frequently asked questions

How do you calculate a due date?

The most common method adds about 280 days to the first day of the last period. Conception or ultrasound dating can also be used.

Which date should I enter?

Enter the first day of the last period, not the last day.

Why is cycle length requested?

A shorter or longer cycle can shift ovulation timing and therefore the expected date.

Is the due date reliable?

It is useful as a benchmark, but remains estimated. Many births happen before or after.

What is the difference between gestational weeks and pregnancy weeks?