Enter values and select Calculate to see your result.
Estimate a due date and gestational age from your last period
Uses 280 days from the last menstrual period, adjusted for cycle length. Clinical dating or ultrasound may differ; this estimate does not assess pregnancy health.
How to use the Pregnancy Calculator
Estimate due date and gestational age from last menstrual period and average cycle length.
- Enter the first day of the last menstrual period.
- Add average cycle length when it differs from 28 days.
- Choose an assessment date and calculate.
Pregnancy Calculator formula
Due date = last period + 280 days + (cycle length − 28 days).
Worked example
Inputs: Last period January 1, 2026, 28-day cycle, assessed April 1, 2026.
What to expect: The estimate is October 8, 2026, with gestational age for the assessment date.
How to read your result
Due dates are estimates; clinical dating and ultrasound may differ.
Frequently asked questions
Is the date exact?
No. Only a small percentage of babies arrive on the estimated date.
When should I contact a clinician?
Use a qualified healthcare professional for dating, symptoms and care decisions.