Pregnancy Due Date Calculator
It estimates a due date from the first day of your last menstrual period and tracks gestational weeks, trimester and milestones.
Estimated due date
Mar 3, 2027
Trimester 1 · 25% complete
Gestational age
10w 0d
Conception (est.)
Jun 10, 2026
Trimester
1
1st trimester ends
Sep 1, 2026
2nd trimester ends
Dec 8, 2026
Days remaining
210
What it calculates
It estimates a due date from the first day of your last menstrual period and tracks gestational weeks, trimester and milestones.
Why it matters
Nearly all antenatal scheduling — scans, screening windows, maternity leave — keys off the estimated due date.
Who it's for
Expectant parents and anyone planning around a pregnancy timeline.
Formula
- LMP
- First day of the last menstrual period
- EDD
- Estimated due date
Worked example
LMP on 1 March
- 1Naegele's rule: LMP + 280 days
- 2Equivalently: −3 months, +7 days, +1 year
Estimated due date 6 December
How the pregnancy due date calculator works
Naegele's rule adds 280 days (40 weeks) to the first day of the last period, assuming a regular 28-day cycle with ovulation on day 14.
Naegele's rule counts 280 days (40 weeks) from the first day of your last menstrual period. Cycles longer or shorter than 28 days shift ovulation, so the estimate adjusts accordingly.
Only about 4% of babies arrive exactly on the due date. An ultrasound dating scan is more accurate, especially with irregular cycles.
Common mistakes
- Counting from the conception date instead of the last period.
- Applying the rule unchanged to irregular or long cycles.
- Treating the due date as a deadline — only about 4% of babies arrive on it.
Tips and best practice
- An early dating scan is more accurate than LMP-based estimates.
- Full term spans 37 to 42 weeks.
Frequently asked questions
How is a due date calculated?
By adding 280 days to the first day of your last menstrual period — Naegele's rule.
How accurate is a due date?
About 4% of births happen on the estimated date; most occur within two weeks either side.
What if my cycle is not 28 days?
Adjust by the difference between your cycle length and 28 days, or use a dating scan.
When do the trimesters start?
First trimester weeks 1–13, second 14–27, third 28 to birth.
Related calculators
Methodology & trust
- Formula source
- Naegele's rule, standard obstetric dating.
- Last updated
- 2026-07-28
- Privacy
- Every calculation runs in your browser. No inputs are sent to a server or stored.
- Accessibility
- Keyboard navigable, labeled inputs and WCAG AA color contrast.