Due Date Calculator
Estimate your pregnancy due date and gestational age
Enter your last menstrual period (LMP) or conception date to estimate your due date, current gestational age, and days remaining. Adjust cycle length for a more personalized result.
How the estimate works
LMP method
Adds 280 days (40 weeks) to the first day of your last period, adjusted for your cycle length.
Conception method
Estimates LMP as 14 days before conception, then applies the standard 280-day calculation.
Cycle adjustment
Cycles shorter or longer than 28 days shift the due date. A 35-day cycle adds 7 days to the estimate.
This is an informational estimate, not medical advice. Only about 5% of babies arrive on the exact due date. Confirm your timeline with your care provider.
Frequently asked questions
Which method is more commonly used?
LMP-based estimation is the standard clinical baseline. Most healthcare providers start with this method before refining with ultrasound.
Can cycle length change the estimate?
Yes. If your cycle is longer or shorter than 28 days, the calculator adjusts the due date accordingly. A 35-day cycle shifts the estimate by about a week.
How accurate is a due date calculator?
Only about 5% of babies arrive on their exact due date. Most births occur within 2 weeks before or after. Use this as a planning guide, not a precise prediction.
Is this a medical diagnosis tool?
No. This calculator is for planning and awareness only. Always confirm your timeline with a qualified healthcare provider.
What if I don't know my last period date?
Use the conception date method instead. If you know the approximate date of conception, the calculator can estimate your due date from that. An early ultrasound can also establish gestational age.
How many weeks is a full-term pregnancy?
A full-term pregnancy is 39 to 40 weeks (273 to 280 days from LMP). Babies born between 37 and 42 weeks are generally considered within the normal range.
What are the trimesters of pregnancy?
The first trimester covers weeks 1-12, the second trimester weeks 13-27, and the third trimester weeks 28-40. Each trimester brings different developmental milestones.
How does an ultrasound due date differ from an LMP due date?
An ultrasound measures the baby directly and can be more accurate, especially in early pregnancy. If the ultrasound date differs by more than a week from the LMP estimate, your provider may adjust the due date.
What is gestational age vs. fetal age?
Gestational age counts from the first day of your last period and is about 2 weeks longer than fetal age, which counts from the actual date of conception.
Can stress or lifestyle affect my due date?
Your due date is a fixed estimate based on conception timing. However, factors like health, nutrition, and stress can influence when labor actually begins, which is why most births occur within a 4-week window around the due date.
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This calculator is for informational purposes only and does not constitute legal, financial, or tax advice. Results are based on publicly available data and rules current at the time of the last update. For specific decisions, consult the relevant authority or a licensed professional. ProperCalc accepts no liability for any inaccuracies or consequences arising from the use of these results.