Pregnancy Week Calculator

Get an instant estimate of your pregnancy week by subtracting the date of your last menstrual period from today's date. The calculator converts the difference into gestational weeks, helping you align appointments, ultrasounds, and trimester milestones.

Enter the four-digit year of the first day of your last menstrual period.
Use 1-12 where January equals 1 and December equals 12.
Provide the calendar day the period started.
Use the current year for today's check-in date.
Month number for the date you are calculating from.
Day of the month for the calculation date.

For informational purposes only. Consult a medical professional for pregnancy guidance.

Examples

  • LMP 2024-01-08, checked on 2024-03-15 ⇒ 9.57 weeks (about 9 weeks 4 days)
  • LMP 2024-06-01, checked on 2024-07-20 ⇒ 7.00 weeks pregnant

FAQ

Why is the last menstrual period used for dating?

Healthcare providers commonly count gestational age from the first day of the last menstrual period because ovulation typically occurs about two weeks later.

Does the calculator adjust for cycle length variations?

No. If your cycles are significantly shorter or longer than 28 days, discuss alternative dating methods such as ultrasound measurements with your clinician.

Can I enter future dates?

You can, but a future 'current date' will return a negative number indicating the event has not occurred yet.

Is this tool a medical diagnosis?

No. Use it for educational planning only and confirm gestational age with a qualified healthcare provider.

How often should I recalculate?

Update the current date whenever you want to know the exact week and day—many parents check weekly to follow fetal development guides.

Additional Information

  • Results display decimal weeks; multiply the digits after the decimal by 7 to convert them into days.
  • The calculation assumes a standard 280-day pregnancy counted from the last menstrual period.

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