# Pregnancy Due Date Calculator

Calculate your estimated pregnancy due date using Naegele's rule. Find your gestational age, trimester, and weeks remaining based on your last menstrual.

## What this calculates

Estimate your baby's due date based on the first day of your last menstrual period (LMP) using Naegele's rule. This widely-used method calculates the due date as 280 days (40 weeks) from your LMP, with an adjustment for cycle length.

## Inputs

- **Days Since Last Menstrual Period (LMP)** (days) — min 0, max 300 — Enter the number of days since the first day of your last menstrual period. For example, if your LMP started 4 weeks ago, enter 28.
- **Average Cycle Length** (days) — min 20, max 45 — Average menstrual cycle length in days (default is 28). This adjusts the due date for longer or shorter cycles.

## Outputs

- **Estimated Days Until Due Date** — Number of days remaining until estimated due date
- **Current Gestational Age** — formatted as text — How far along the pregnancy is in weeks and days
- **Current Trimester** — formatted as text — Which trimester of pregnancy
- **Weeks Remaining** — Approximate weeks until due date
- **Important Note** — formatted as text — Disclaimer about due date estimation

## Details

Naegele's rule, developed by German obstetrician Franz Naegele in 1812, is the standard method for estimating pregnancy due dates. The formula adds 280 days (40 weeks) to the first day of the last menstrual period, assuming a 28-day cycle. For women with longer or shorter cycles, the estimated date is adjusted accordingly, since ovulation typically occurs 14 days before the next period. While widely used, only about 5% of babies are born on their exact due date. A full-term pregnancy ranges from 37 to 42 weeks. First-trimester ultrasound is considered the most accurate method for pregnancy dating and may adjust the due date if it differs significantly from the LMP-based estimate.

## Frequently Asked Questions

**Q: How accurate is Naegele's rule?**

A: Naegele's rule provides a useful estimate, but only about 5% of babies are born on the exact due date. The majority of full-term babies are born within 2 weeks before or after the estimated date. First-trimester ultrasound dating is generally more accurate, especially for women with irregular cycles.

**Q: Why does cycle length matter?**

A: Naegele's rule assumes a 28-day cycle with ovulation on day 14. If your cycle is longer or shorter, ovulation likely occurs on a different day. The calculator adjusts for this by adding or subtracting the difference from 28 days, providing a more accurate estimate for women with non-standard cycle lengths.

**Q: What if I don't know the exact date of my last period?**

A: If you are unsure of your LMP date, an ultrasound in the first trimester (before 13 weeks) is the most reliable way to date a pregnancy. Consult your healthcare provider for an accurate assessment.

**Q: Is this calculator a substitute for prenatal care?**

A: Absolutely not. This calculator is for informational purposes only. Prenatal care from a qualified obstetrician or midwife is essential for monitoring both maternal and fetal health throughout pregnancy. Always consult your healthcare provider for accurate pregnancy dating and care.

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Source: https://vastcalc.com/calculators/health/pregnancy-due-date
Category: Health & Fitness
Last updated: 2026-04-21