How to Calculate Weeks Pregnant
What is Weeks Pregnant?
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.
Formula
Step-by-Step Guide
- 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
Frequently Asked Questions
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.
Ready to calculate? Try the free Weeks Pregnant Calculator
Try it yourself →