What this tool does
The Pregnancy Due Date Calculator estimates your expected delivery date (EDD) based on the first day of your last menstrual period (LMP). It applies Naegele's Rule, the standard method used by obstetricians worldwide, which calculates the due date as 280 days (40 weeks) from the LMP. The calculator also adjusts for non-standard cycle lengths, since women with cycles shorter or longer than 28 days will ovulate at different times. Beyond the due date, the tool displays your current gestational age in weeks and days, identifies which trimester you are in, counts down the remaining days, estimates your conception date, and presents a visual timeline of key pregnancy milestones from first heartbeat through full term.
How it calculates
The calculator uses Naegele's Rule, the gold standard for estimating due dates:
**EDD = LMP + 280 days + (cycle length - 28)**
Where: - **EDD** is the Estimated Due Date - **LMP** is the first day of the Last Menstrual Period - **280 days** equals 40 weeks, the standard gestational period - **Cycle adjustment** accounts for variation from the typical 28-day cycle
For cycle length adjustment, ovulation typically occurs 14 days before the next period. A 32-day cycle means ovulation on day 18 instead of day 14, so the due date shifts 4 days later. The conception date is estimated as LMP + (cycle length - 14) days, since the luteal phase is consistently about 14 days regardless of cycle length.
Trimester boundaries are: First trimester (weeks 1-12), Second trimester (weeks 13-27), Third trimester (weeks 28-40).
Who should use this
- Women who have just learned they are pregnant and want a quick due date estimate before their first prenatal appointment - Partners and family members planning around an expected delivery date for work leave or travel - Women with irregular cycles who want to see how cycle length affects the estimated due date - Anyone tracking pregnancy progress who wants to see current gestational age and upcoming milestones
Worked examples
**Example 1: Standard 28-day cycle** A woman's LMP was January 1, 2026, with a standard 28-day cycle. - EDD = January 1 + 280 days = October 8, 2026 - If today is March 15, gestational age = 73 days = 10 weeks 3 days (first trimester) - Days remaining = 207 - Conception date estimate = January 1 + 14 = January 15, 2026
**Example 2: Longer 32-day cycle** A woman's LMP was February 10, 2026, with a 32-day cycle. - Cycle adjustment = 32 - 28 = +4 days - EDD = February 10 + 284 days = November 21, 2026 - Conception date estimate = February 10 + (32 - 14) = March 10, 2026
**Example 3: Shorter 25-day cycle** A woman's LMP was March 5, 2026, with a 25-day cycle. - Cycle adjustment = 25 - 28 = -3 days - EDD = March 5 + 277 days = December 7, 2026 - The due date shifts earlier because ovulation occurred sooner in the cycle
Limitations
- Naegele's Rule assumes a regular menstrual cycle and may be inaccurate for women with highly irregular periods or conditions like PCOS - Only about 5% of babies are born on their exact due date; most deliveries occur between 38 and 42 weeks - The calculator cannot replace ultrasound dating, which is more accurate especially in the first trimester - It does not account for factors like maternal age, medical conditions, or multiple pregnancies (twins, triplets) that affect delivery timing - Women who conceived through IVF should use their embryo transfer date rather than LMP for due date calculation
FAQs
Q: How accurate is Naegele's Rule? A: Naegele's Rule provides a good estimate, but only about 5% of babies arrive on the exact due date. It is most accurate for women with regular 28-day cycles. First-trimester ultrasound is considered more precise, with accuracy within 5-7 days.
Q: Why does cycle length affect the due date? A: Cycle length affects when ovulation occurs. The luteal phase (post-ovulation) is consistently about 14 days, so a longer cycle means later ovulation and a later due date. A 35-day cycle shifts the due date 7 days later than a 28-day cycle.
Q: What if I do not know my exact LMP date? A: If you are unsure of your LMP, an early ultrasound (ideally 8-12 weeks) can estimate gestational age based on the baby's size. This is often more accurate than date-based calculations for women with irregular cycles.
Q: Can this calculator be used for twins or multiples? A: This calculator estimates a standard singleton pregnancy. Twin pregnancies typically deliver earlier (around 36-37 weeks on average), and your healthcare provider will adjust your timeline accordingly.
Explore Similar Tools
Explore more tools like this one:
- Pregnancy Due Date — Estimate your baby's due date based on the date of your... - Pregnancy Calculator — Calculate pregnancy milestones, trimester dates, and... - Due Date Calculator — Calculate your baby's due date based on last menstrual... - Pregnancy Conception Calculator — Calculate the estimated conception date based on due... - Pregnancy Weight Gain Calculator — Calculate recommended pregnancy weight gain based on...