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Weeks Pregnant Calculator

First Day of Last Menstrual Period

What is Weeks Pregnant Calculator?

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Pregnancy is counted in weeks from the first day of the Last Menstrual Period (LMP). Full term is 40 weeks. Babies born 37–42 weeks are considered full term.

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f(x)Weeks gestation = (Current date − LMP) / 7 | Due date = LMP + 280 days

How to Weeks Pregnant Calculator

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1Weeks = (Today − LMP) / 7
2Due date = LMP + 280 days (Naegele's rule)
3First trimester: 1–13 weeks; Second: 14–27; Third: 28–40
4Preterm: born before 37 weeks

Worked Examples

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Example 1

Given:LMP 1 January, checking 1 April

Výsledok:13 weeks pregnant; second trimester begins next week

Real-World Applications

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Calculating deadlines and project timelines

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Determining exact ages for legal or medical purposes

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Planning events and scheduling across time zones

Pregnancy Trimesters

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Trimester	Weeks	Key events
First	1–13	Organ formation; highest miscarriage risk
Second	14–27	Anatomy scan; fetal movement
Third	28–40	Rapid growth; birth preparation

Frequently Asked Questions

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What is Weeks Pregnant?

Pregnancy is counted in weeks from the first day of the Last Menstrual Period (LMP). Full term is 40 weeks

How accurate is the Weeks Pregnant calculator?

The calculator uses the standard published formula for weeks pregnant. Results are accurate to the precision of the inputs you provide. For financial, medical, or legal decisions, always verify with a qualified professional.

What units does the Weeks Pregnant calculator use?

This calculator works with inches, watts. You can enter values in the units shown — the calculator handles all conversions internally.

What formula does the Weeks Pregnant calculator use?

The core formula is: Weeks = (Today − LMP) / 7. Each step in the calculation is shown so you can verify the result manually.

References

›Pregnancy week by week — NHS

Len na informačné účely. Tento nástroj nenahrádza odborné lekárske poradenstvo, diagnózu ani liečbu. Vždy sa poraďte s kvalifikovaným zdravotníckym odborníkom.

Accuracy-checked

Reviewed October 2026

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