Pregnancy Week & Trimester Calculator

Pregnancy week, trimester, and weeks-until-due from LMP. Not medical advice.

Inputs

Result

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General calculation reads

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How to use this calculator

  • Enter LMP.
  • Set "as of" to today.
  • Read week, trimester, and weeks-to-due.

About this calculator

Pregnancy is conventionally measured from LMP. A standard pregnancy is 280 days (40 weeks) from LMP. Trimesters: 1st (0-12 weeks), 2nd (13-26), 3rd (27-birth). Most births happen between week 38 and 42; "term" is 37+ weeks. Not medical advice — work with a qualified provider.

Frequently asked

Why 40 weeks?+
Naegele's Rule: LMP + 280 days. Conventional in US, UK, and most of the world. Some countries use LMP + 282 days.
Are the trimester boundaries exact?+
No — slightly different sources give slightly different cutoffs. Common: week 13 starts 2nd, week 27 starts 3rd.
What's "term" pregnancy?+
Usually 37+ weeks. Specifically: early term 37-38, full term 39-40, late term 41, post-term 42+.
Medical advice?+
No — this is a date calculator. Prenatal care, anomaly screening, and birthing decisions should always involve a qualified provider.
How is this different from gestation-calculator?+
Same math. This one frames the output around weeks/trimester/due date; gestation-calculator focuses on weeks+days for clinical use.

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