Pregnancy Calculator
Estimate a due date, current pregnancy week, and trimester based on the last menstrual period (LMP); general guide only.
Inputs
Result
Enter values on the left and select Calculate to see the result here.
What the Pregnancy Calculator does
- Estimates a due date from the last menstrual period (LMP) date you enter.
- Shows a general pregnancy week and trimester timeline based on your inputs and today’s date.
- Provides a date estimate only; it does not confirm pregnancy, diagnose complications, or replace medical care.
How to use the Pregnancy Calculator
- Enter the first day of the last menstrual period (LMP).
- Click Calculate to see the estimated due date, current pregnancy week, and trimester based on your inputs.
- Use the result as a general guide and confirm pregnancy dating and care plans with a midwife, GP, doctor, or qualified healthcare professional.
Formula / methodology used
- The estimated due date uses Naegele’s rule: LMP + 280 days, or 40 weeks.
- Current week is calculated from days since the LMP date, then grouped into trimesters.
- Clinical pregnancy dating can vary based on cycle length, ovulation timing, ultrasound dating, embryo transfer date, and healthcare professional assessment.
Example calculation
Last menstrual period start date: 2026-01-01.
- Estimated due date = 2026-01-01 + 280 days = 2026-10-08
- Pregnancy week is estimated from the number of days between 2026-01-01 and today
- Trimester is assigned from the estimated week: weeks 1–13 first, 14–27 second, and 28+ third
Result: Based on an LMP of 2026-01-01, the calculator would show an estimated due date of 2026-10-08. The displayed week and trimester depend on today’s date.
Common mistakes and limitations
- The calculator assumes a standard 280-day pregnancy measured from LMP, which may not match every pregnancy.
- It does not adjust for cycle length, irregular periods, known ovulation date, ultrasound dating, embryo transfer date, or clinical risk factors.
- It does not confirm pregnancy, detect miscarriage or ectopic pregnancy, diagnose complications, or provide emergency guidance.
- Always use professional medical advice for pregnancy care, symptoms, medication decisions, fertility treatment, or concerns about your health or your baby.
Important note
This pregnancy calculator provides an estimated due date and general timeline based on your inputs. It is not medical advice, does not confirm pregnancy, and does not diagnose pregnancy complications. Speak to a midwife, GP, doctor, obstetric clinician, fertility clinic, or other qualified healthcare professional for personal pregnancy care.
Pregnancy Calculator FAQs
Is the estimated due date exact?
No. A due date is an estimate, and many births happen before or after the estimated due date.
Does this calculator confirm pregnancy?
No. It does not confirm pregnancy, diagnose pregnancy complications, or assess your health. Contact a healthcare professional for pregnancy testing, antenatal care, symptoms, bleeding, pain, or urgent concerns.
Why might my healthcare provider give a different due date?
Dating can vary because of cycle length, ovulation timing, ultrasound measurements, embryo transfer date, and clinical assessment. Your healthcare provider’s dating may be more appropriate for your care.
Who should I contact for pregnancy care?
Contact a midwife, GP, doctor, obstetric clinician, fertility clinic, or qualified healthcare professional for pregnancy care, medication questions, symptoms, or medical concerns.