Pregnancy Due Date Calculator
Estimate when your baby is due from the first day of your last menstrual period. Adjust for your cycle length to see your estimated due date, how many weeks along you are and which trimester you are in.
How to use the due date calculator
- Enter the first day of your last menstrual period.
- Adjust the average cycle length if yours is not 28 days.
- Read your estimated due date, weeks along and current trimester.
Examples
Average 28-day cycle
Last period started 2024-01-01
Due date 2024-10-07 (280 days later)
Longer 35-day cycle
Last period started 2024-01-01, 35-day cycle
Due date 2024-10-14 (shifted 7 days later)
Frequently asked questions
How is the due date calculated?
It uses Naegele's rule: the estimated due date is 280 days (40 weeks) from the first day of your last menstrual period. If your cycle is not 28 days, the date is shifted by the difference, since a longer cycle means later ovulation.
How accurate is a due date from the last period?
It is an estimate. Only about 4 in 100 babies arrive on the exact due date, and most births happen within two weeks either side. An early ultrasound dating scan is usually more precise.
Why does cycle length matter?
Naegele's rule assumes ovulation on day 14 of a 28-day cycle. If your cycle is longer or shorter, you ovulate later or earlier, so the calculator shifts the due date by your cycle length minus 28 days.
How are weeks along and trimester worked out?
Gestational age is counted from the first day of your last period, so you start at week 0. The first trimester runs to week 13, the second to week 27, and the third from week 27 to birth.
Is this a substitute for medical advice?
No. This is an estimate for planning only. Please confirm your due date with your doctor or midwife, who can use an ultrasound and your full history.
Is my information kept private?
Yes. The calculation runs entirely in your browser. The dates you enter are never uploaded or stored.
Related tools
BMI Calculator
Free BMI calculator. Enter your weight and height in metric or imperial units to get your Body Mass Index and WHO weight category instantly.
BAC Calculator
Estimate your blood alcohol concentration with the Widmark formula. Enter weight, sex, drinks and hours. An estimate only, never a reason to drive.
A1C to Glucose Converter
Convert A1C to estimated average glucose and back, in mg/dL and mmol/L, using the ADA eAG formula. Enter either value and see the match live.
Blood Pressure Category
Enter your systolic and diastolic numbers to find your blood pressure category using the AHA/ACC 2017 chart, from Normal to Hypertensive Crisis.
BMR Calculator
Calculate your basal metabolic rate (BMR) with the Mifflin-St Jeor equation. Enter weight, height, age and sex to see calories burned at rest per day.
Body Fat Calculator
Estimate your body fat percentage with the US Navy tape method. Enter height, neck and waist (plus hip for women) to see your body fat and category.