How to Calculate Your Pregnancy Due Date
Automated technical check: . Scope and review policy
The Pregnancy Due Date Calculator adds 280 calendar days to the first day of the last menstrual period (LMP). This is an estimated calendar date, not a prediction of when delivery will occur. It assumes a 28-day cycle with ovulation around day 14; the tool does not assess whether that assumption fits a particular pregnancy.
A reproducible example
With LMP November 10, 2025, the estimate is Monday, August 17, 2026. On the fixed comparison date January 19, 2026, 70 calendar days have passed: 10 completed weeks and 0 days. There are 210 calendar days to the estimated date. The live tool compares your LMP with today's local calendar date, so its weeks-along result changes over time.
Adding days is not the same as adding an elapsed number of hours across daylight-saving changes. DigiCalc uses calendar dates for this calculation; a spring or autumn clock change cannot move the due date. Adding a year, subtracting three months and adding seven days can differ from exactly 280 days because calendar months vary in length. The implemented rule is explicitly LMP plus 280 days.
What dates are supported?
Enter the first day of the last period, not the day the period ended. The tool accepts a valid LMP on or before today within the last year. That one-year limit is a software input boundary, not a statement about pregnancy duration. Impossible dates or a future LMP show no result.
There is no conception-date input, cycle-length adjustment, IVF transfer input or ultrasound-redating calculation. The displayed LMP-plus-14-days conception estimate is illustrative only, not a determination of conception. Use your clinician's established dating for medical decisions, particularly when LMP is uncertain or assisted reproduction is involved.
Read weeks and term labels correctly
Calendar weeks are counted from LMP: 13 weeks and 6 days precedes 14 completed weeks. The tool starts its second-trimester display at week 14 and its third at week 28. These are timeline conventions, not appointment recommendations.
| Term | Gestational age |
|---|---|
| Early term | 37 weeks through 38 weeks, 6 days |
| Full term | 39 weeks through 40 weeks, 6 days |
| Late term | 41 weeks through 41 weeks, 6 days |
| Postterm | 42 weeks and beyond |
The estimate does not provide a prenatal test schedule, assess symptoms or determine a delivery plan. A date after the estimated due date is shown as days past that estimate, not as a diagnosis. Bring questions about dating or care to your maternity care team.
Sources and Scope
Technical example checks are not independent professional review. Sources were checked for the statements above on October 6, 2026.