# Pregnancy Due Date Calculator

> Calculate your expected due date based on your last menstrual period using Naegele's Rule.

**Category:** Health
**Keywords:** pregnancy, due date, baby, naegele, trimester, gestation, expected delivery, EDD
**URL:** https://complete.tools/pregnancy-due-date-calculator

## 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.

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*Generated from [complete.tools/pregnancy-due-date-calculator](https://complete.tools/pregnancy-due-date-calculator)*