Pregnancy Due Date Calculator
Estimate baby due date, gestational age in weeks and days, and trimester milestones using Naegele rule.
About Pregnancy Due Date Calculator
Expecting parents and healthcare providers calculate estimated delivery dates (EDD) to monitor fetal development milestones, schedule ultrasound screenings, and prepare for labor. Because conception dates are rarely known with absolute certainty, clinical obstetrics relies on standardized menstrual cycle calculations.
Naegele rule is the gold standard clinical formula used worldwide to estimate delivery dates from the first day of the last menstrual period (LMP). Applying manual calendar arithmetic across varying month lengths frequently causes math mistakes.
This in-browser pregnancy due date calculator evaluates gestational age and estimated delivery dates using Naegele rule and cycle length adjustments. It provides week-by-week developmental progress indicators and key trimester dates.
To track gestational milestones, calculate calendar intervals with the date difference calculator and maintain wellness with the daily water intake calculator.
Step-by-step practical guide
- Select your calculation basis: First Day of Last Menstrual Period (LMP), Exact Conception Date, or IVF Embryo Transfer Date.
- Enter the corresponding date into the calendar picker.
- Specify your typical menstrual cycle length, which defaults to the clinical standard of 28 days.
- Click Calculate Due Date to view your estimated delivery date and gestational age in weeks and days.
- Examine the trimester roadmap showing completion dates for Trimester 1, Trimester 2, and Trimester 3.
- Review the countdown indicator displaying remaining weeks until your estimated delivery date.
Engineering specifications and execution details
Implements Naegele rule: EDD = LMP + 1 year - 3 months + 7 days (equivalent to LMP + 280 days for a standard 28-day cycle).
Adjusts for non-standard cycle lengths: Adds or subtracts (Cycle Length - 28 days) to account for earlier or later ovulation.
Calculates IVF transfer dates: EDD = Transfer Date + 266 days - embryo age (3-day or 5-day blastocyst).
Delineates trimesters: Trimester 1 (Weeks 1 to 13), Trimester 2 (Weeks 14 to 27), Trimester 3 (Weeks 28 to 40+).
Executes all calendar date mathematics locally using browser native Date objects.
Data privacy and memory isolation
Personal health details, cycle history, and family planning dates remain private on your computer.
No medical data or tracking cookies are logged or transmitted to third parties.
Common production use cases
- Expecting mothers and partners planning maternity leave timelines and nursery preparations.
- Obstetric nurses and doulas conducting preliminary gestational age screenings during intake calls.
- Couples tracking embryonic development milestones week by week throughout pregnancy.
- Patients undergoing in vitro fertilization (IVF) calculating delivery dates based on blastocyst transfer days.
- Healthcare students learning standard obstetrical calculation formulas and cycle length adjustments.
Edge cases and operational boundaries
- Irregular cycles: Women with cycle lengths fluctuating beyond 35 days should consult a clinical ultrasound scan for accurate dating.
- Leap years: February 29 calendar calculations are handled automatically by native Date arithmetic.
- Multiple gestations: Twins and triplets typically deliver earlier (average 36 weeks for twins), which clinicians monitor separately.
- Actual delivery variance: Only about 4 to 5 percent of babies are born on their exact calculated due date; most arrive between 37 and 42 weeks.
Frequently Asked Questions
What is Naegele rule for calculating pregnancy due dates?
Naegele rule calculates estimated due date (EDD) by taking the first day of the last menstrual period (LMP), adding one year, subtracting three months, and adding seven days.
How accurate is an estimated due date calculated from LMP?
LMP provides a reliable clinical estimate assuming a standard 28-day menstrual cycle with ovulation occurring on day 14. First-trimester ultrasound measurements refine this baseline.
What if my menstrual cycle is longer than 28 days?
If your cycle is 35 days, ovulation occurred approximately on day 21 (7 days later than average), shifting your estimated delivery date roughly one week forward.
How does an ultrasound due date compare to an LMP due date?
A crown-rump length (CRL) ultrasound performed between 8 and 13 weeks has an accuracy window of plus or minus 5 days, overriding LMP calculations if discrepancies exceed 7 days.
What are the exact weeks for each trimester?
First trimester spans week 1 through week 13; Second trimester spans week 14 through week 27; Third trimester spans week 28 through week 40 and beyond.
Can this tool be used for IVF embryo transfers?
Yes. For IVF pregnancies, calculating from the exact embryo transfer date (adding 266 days for Day 3 transfers or 263 days for Day 5 blastocysts) gives precise due dates.
How many days long is a standard full-term human pregnancy?
A full-term pregnancy lasts approximately 280 days (40 weeks or 10 lunar months) calculated from the first day of the last menstrual period (LMP).
What percentage of babies are actually born on their exact due date?
Only about 4% to 5% of babies arrive on their exact predicted delivery date, while approximately 90% arrive within two weeks before or after the estimated date.
What is the difference between gestational age and fetal age?
Gestational age measures pregnancy from the first day of the last menstrual period, whereas fetal age (conceptional age) measures from actual fertilization, typically two weeks later.