Pregnancy Calculator
Estimate your due date, pregnancy week, trimester, and important dates based on your last menstrual period.
Estimated Pregnancy Results
These are calendar estimates based on the LMP date, not a clinical assessment.
What Is a Pregnancy Calculator?
A pregnancy calculator estimates gestational age and an expected due date using the first day of the last menstrual period (LMP).
Pregnancy dating is commonly calculated from the first day of the last menstrual period. A typical estimated due date is 280 days, or 40 weeks, from that date.
How to Use This Pregnancy Calculator
- Find the first day of your last menstrual period.
- Enter that date in the date field.
- Select Calculate Pregnancy.
- Review your estimated due date, gestational age, and trimester.
Understanding Pregnancy Trimesters
For this calculator, the trimesters are estimated using these gestational-age ranges:
- First trimester: before 14 completed weeks.
- Second trimester: from 14 completed weeks to before 28 completed weeks.
- Third trimester: from 28 completed weeks onward.
Definitions of trimester boundaries can vary slightly between resources. The calculator uses completed gestational weeks to select a trimester.
How Accurate Is the Estimated Due Date?
A due date calculated from the LMP assumes that the date is known and that cycle timing is reasonably typical. Ovulation does not occur on the same day for everyone, so the conception estimate may be inaccurate. A healthcare professional may revise pregnancy dating using menstrual history and ultrasound findings.
Frequently Asked Questions
How is the estimated due date calculated?
The conventional LMP method adds 280 days, or 40 weeks, to the first day of the last menstrual period.
Is the pregnancy due date exact?
No. It is an estimate, not a guaranteed birth date. Birth can occur before or after the estimated due date.
How is gestational age different from conception age?
Gestational age is conventionally counted from the first day of the last menstrual period. Conception usually occurs later, but its timing varies.
What if I do not know my last menstrual period?
If you do not know your LMP or your cycles are irregular, consult a healthcare professional to discuss appropriate pregnancy dating.
Can this calculator predict the exact birth date?
No. It estimates a due date from menstrual dates. It cannot predict the exact day a baby will be born.
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