pregnancy calculator

Professional pregnancy calculator that estimates due date (EDD), current gestational age, and trimester milestones using LMP, conception/IVF, or ultrasound dating. WCAG 2.1 AA accessible.

Full original guide (expanded)

Data Source & Methodology

AuthoritativeDataSource:

Tutti i calcoli si basano rigorosamente sulle formule e sui dati forniti da questa fonte.

The Formula Explained

LMP method (Naegele’s rule, 28-day cycle):

$$ \mathrm{EDD} = \mathrm{LMP} + 280 \ \text{days} $$

Adjusted for cycle length \(C\) (days):

Ovulation \(= \mathrm{LMP} + (C - 14)\) days; then $$ \mathrm{EDD} = \mathrm{Ovulation} + 266 \ \text{days}. $$

Conception known: $$ \mathrm{EDD} = \mathrm{Conception} + 266 \ \text{days}. $$

IVF transfers: 3-day: \( \mathrm{EDD} = \mathrm{Transfer} + 263\ \text{days} \) ; 5-day: \( \mathrm{EDD} = \mathrm{Transfer} + 261\ \text{days} \).

Ultrasound dating: Given scan date \(D_s\) and gestational age at scan \(GA_s\) (days),

$$ \mathrm{EDD} = D_s + (280 - GA_s)\ \text{days}. $$

Glossary of Variables

  • LMP: First day of the last menstrual period.
  • Cycle length (C): Days from first day of one period to the day before the next (default 28).
  • Conception/Transfer date: Date of fertilization or embryo transfer (IVF).
  • EDD: Estimated Due Date.
  • GA: Gestational Age in weeks+days since LMP-based start.

How It Works: A Step-by-Step Example

Scenario: LMP = 2025-02-01, cycle length = 30 days.

  1. Approximate ovulation = LMP + (30 − 14) = 2025-02-17.
  2. EDD = ovulation + 266 days = 2025-11-10.
  3. On 2025-10-30 (today), GA ≈ 37w4d, approaching early term (≥37w0d).

Frequently Asked Questions

Which method is most accurate?

First-trimester ultrasound is generally most precise. Known conception/IVF is also reliable. LMP assumes regular ovulation timing.

My cycles are irregular—what should I use?

Prefer ultrasound dating. If using LMP, understand the margin of error may be higher.

Why is the EDD a single day if birth rarely happens that day?

EDD is the center of a normal distribution; most births occur within ±2 weeks of the EDD.

Can the due date change after a later scan?

Professionals avoid changing EDD after reliable early ultrasound unless the discrepancy is large.

What are term categories?

Early term: 37w0d–38w6d; Full term: 39w0d–40w6d; Late term: 41w0d–41w6d; Postterm: ≥42w.

Is this medical advice?

No. This tool is educational and should not replace professional clinical judgment.

Last accuracy review:

Audit: Complete
Formula (LaTeX) + variables + units
This section shows the formulas used by the calculator engine, plus variable definitions and units.
Formula (extracted LaTeX)
\[\mathrm{EDD} = \mathrm{LMP} + 280 \ \text{days}\]
\mathrm{EDD} = \mathrm{LMP} + 280 \ \text{days}
Formula (extracted LaTeX)
\[\mathrm{EDD} = \mathrm{Ovulation} + 266 \ \text{days}.\]
\mathrm{EDD} = \mathrm{Ovulation} + 266 \ \text{days}.
Formula (extracted LaTeX)
\[\mathrm{EDD} = \mathrm{Conception} + 266 \ \text{days}.\]
\mathrm{EDD} = \mathrm{Conception} + 266 \ \text{days}.
Formula (extracted LaTeX)
\[\mathrm{EDD} = D_s + (280 - GA_s)\ \text{days}.\]
\mathrm{EDD} = D_s + (280 - GA_s)\ \text{days}.
Formula (extracted text)
LMP method (Naegele’s rule, 28-day cycle): $ \mathrm{EDD} = \mathrm{LMP} + 280 \ \text{days} $ Adjusted for cycle length \(C\) (days): Ovulation \(= \mathrm{LMP} + (C - 14)\) days; then $ \mathrm{EDD} = \mathrm{Ovulation} + 266 \ \text{days}. $ Conception known: $ \mathrm{EDD} = \mathrm{Conception} + 266 \ \text{days}. $ IVF transfers: 3-day: \( \mathrm{EDD} = \mathrm{Transfer} + 263\ \text{days} \) ; 5-day: \( \mathrm{EDD} = \mathrm{Transfer} + 261\ \text{days} \). Ultrasound dating: Given scan date \(D_s\) and gestational age at scan \(GA_s\) (days), $ \mathrm{EDD} = D_s + (280 - GA_s)\ \text{days}. $
Variables and units
  • No variables provided in audit spec.
Sources (authoritative):
Changelog
Version: 0.1.0-draft
Last code update: 2026-01-19
0.1.0-draft · 2026-01-19
  • Initial audit spec draft generated from HTML extraction (review required).
  • Verify formulas match the calculator engine and convert any text-only formulas to LaTeX.
  • Confirm sources are authoritative and relevant to the calculator methodology.
Verified by Ugo Candido on 2026-01-19
Profile · LinkedIn

Data Source & Methodology

AuthoritativeDataSource:

Tutti i calcoli si basano rigorosamente sulle formule e sui dati forniti da questa fonte.

The Formula Explained

LMP method (Naegele’s rule, 28-day cycle):

$$ \mathrm{EDD} = \mathrm{LMP} + 280 \ \text{days} $$

Adjusted for cycle length \(C\) (days):

Ovulation \(= \mathrm{LMP} + (C - 14)\) days; then $$ \mathrm{EDD} = \mathrm{Ovulation} + 266 \ \text{days}. $$

Conception known: $$ \mathrm{EDD} = \mathrm{Conception} + 266 \ \text{days}. $$

IVF transfers: 3-day: \( \mathrm{EDD} = \mathrm{Transfer} + 263\ \text{days} \) ; 5-day: \( \mathrm{EDD} = \mathrm{Transfer} + 261\ \text{days} \).

Ultrasound dating: Given scan date \(D_s\) and gestational age at scan \(GA_s\) (days),

$$ \mathrm{EDD} = D_s + (280 - GA_s)\ \text{days}. $$

Glossary of Variables

  • LMP: First day of the last menstrual period.
  • Cycle length (C): Days from first day of one period to the day before the next (default 28).
  • Conception/Transfer date: Date of fertilization or embryo transfer (IVF).
  • EDD: Estimated Due Date.
  • GA: Gestational Age in weeks+days since LMP-based start.

How It Works: A Step-by-Step Example

Scenario: LMP = 2025-02-01, cycle length = 30 days.

  1. Approximate ovulation = LMP + (30 − 14) = 2025-02-17.
  2. EDD = ovulation + 266 days = 2025-11-10.
  3. On 2025-10-30 (today), GA ≈ 37w4d, approaching early term (≥37w0d).

Frequently Asked Questions

Which method is most accurate?

First-trimester ultrasound is generally most precise. Known conception/IVF is also reliable. LMP assumes regular ovulation timing.

My cycles are irregular—what should I use?

Prefer ultrasound dating. If using LMP, understand the margin of error may be higher.

Why is the EDD a single day if birth rarely happens that day?

EDD is the center of a normal distribution; most births occur within ±2 weeks of the EDD.

Can the due date change after a later scan?

Professionals avoid changing EDD after reliable early ultrasound unless the discrepancy is large.

What are term categories?

Early term: 37w0d–38w6d; Full term: 39w0d–40w6d; Late term: 41w0d–41w6d; Postterm: ≥42w.

Is this medical advice?

No. This tool is educational and should not replace professional clinical judgment.

Last accuracy review:

Audit: Complete
Formula (LaTeX) + variables + units
This section shows the formulas used by the calculator engine, plus variable definitions and units.
Formula (extracted LaTeX)
\[\mathrm{EDD} = \mathrm{LMP} + 280 \ \text{days}\]
\mathrm{EDD} = \mathrm{LMP} + 280 \ \text{days}
Formula (extracted LaTeX)
\[\mathrm{EDD} = \mathrm{Ovulation} + 266 \ \text{days}.\]
\mathrm{EDD} = \mathrm{Ovulation} + 266 \ \text{days}.
Formula (extracted LaTeX)
\[\mathrm{EDD} = \mathrm{Conception} + 266 \ \text{days}.\]
\mathrm{EDD} = \mathrm{Conception} + 266 \ \text{days}.
Formula (extracted LaTeX)
\[\mathrm{EDD} = D_s + (280 - GA_s)\ \text{days}.\]
\mathrm{EDD} = D_s + (280 - GA_s)\ \text{days}.
Formula (extracted text)
LMP method (Naegele’s rule, 28-day cycle): $ \mathrm{EDD} = \mathrm{LMP} + 280 \ \text{days} $ Adjusted for cycle length \(C\) (days): Ovulation \(= \mathrm{LMP} + (C - 14)\) days; then $ \mathrm{EDD} = \mathrm{Ovulation} + 266 \ \text{days}. $ Conception known: $ \mathrm{EDD} = \mathrm{Conception} + 266 \ \text{days}. $ IVF transfers: 3-day: \( \mathrm{EDD} = \mathrm{Transfer} + 263\ \text{days} \) ; 5-day: \( \mathrm{EDD} = \mathrm{Transfer} + 261\ \text{days} \). Ultrasound dating: Given scan date \(D_s\) and gestational age at scan \(GA_s\) (days), $ \mathrm{EDD} = D_s + (280 - GA_s)\ \text{days}. $
Variables and units
  • No variables provided in audit spec.
Sources (authoritative):
Changelog
Version: 0.1.0-draft
Last code update: 2026-01-19
0.1.0-draft · 2026-01-19
  • Initial audit spec draft generated from HTML extraction (review required).
  • Verify formulas match the calculator engine and convert any text-only formulas to LaTeX.
  • Confirm sources are authoritative and relevant to the calculator methodology.
Verified by Ugo Candido on 2026-01-19
Profile · LinkedIn

Data Source & Methodology

AuthoritativeDataSource:

Tutti i calcoli si basano rigorosamente sulle formule e sui dati forniti da questa fonte.

The Formula Explained

LMP method (Naegele’s rule, 28-day cycle):

$$ \mathrm{EDD} = \mathrm{LMP} + 280 \ \text{days} $$

Adjusted for cycle length \(C\) (days):

Ovulation \(= \mathrm{LMP} + (C - 14)\) days; then $$ \mathrm{EDD} = \mathrm{Ovulation} + 266 \ \text{days}. $$

Conception known: $$ \mathrm{EDD} = \mathrm{Conception} + 266 \ \text{days}. $$

IVF transfers: 3-day: \( \mathrm{EDD} = \mathrm{Transfer} + 263\ \text{days} \) ; 5-day: \( \mathrm{EDD} = \mathrm{Transfer} + 261\ \text{days} \).

Ultrasound dating: Given scan date \(D_s\) and gestational age at scan \(GA_s\) (days),

$$ \mathrm{EDD} = D_s + (280 - GA_s)\ \text{days}. $$

Glossary of Variables

  • LMP: First day of the last menstrual period.
  • Cycle length (C): Days from first day of one period to the day before the next (default 28).
  • Conception/Transfer date: Date of fertilization or embryo transfer (IVF).
  • EDD: Estimated Due Date.
  • GA: Gestational Age in weeks+days since LMP-based start.

How It Works: A Step-by-Step Example

Scenario: LMP = 2025-02-01, cycle length = 30 days.

  1. Approximate ovulation = LMP + (30 − 14) = 2025-02-17.
  2. EDD = ovulation + 266 days = 2025-11-10.
  3. On 2025-10-30 (today), GA ≈ 37w4d, approaching early term (≥37w0d).

Frequently Asked Questions

Which method is most accurate?

First-trimester ultrasound is generally most precise. Known conception/IVF is also reliable. LMP assumes regular ovulation timing.

My cycles are irregular—what should I use?

Prefer ultrasound dating. If using LMP, understand the margin of error may be higher.

Why is the EDD a single day if birth rarely happens that day?

EDD is the center of a normal distribution; most births occur within ±2 weeks of the EDD.

Can the due date change after a later scan?

Professionals avoid changing EDD after reliable early ultrasound unless the discrepancy is large.

What are term categories?

Early term: 37w0d–38w6d; Full term: 39w0d–40w6d; Late term: 41w0d–41w6d; Postterm: ≥42w.

Is this medical advice?

No. This tool is educational and should not replace professional clinical judgment.

Last accuracy review:

Audit: Complete
Formula (LaTeX) + variables + units
This section shows the formulas used by the calculator engine, plus variable definitions and units.
Formula (extracted LaTeX)
\[\mathrm{EDD} = \mathrm{LMP} + 280 \ \text{days}\]
\mathrm{EDD} = \mathrm{LMP} + 280 \ \text{days}
Formula (extracted LaTeX)
\[\mathrm{EDD} = \mathrm{Ovulation} + 266 \ \text{days}.\]
\mathrm{EDD} = \mathrm{Ovulation} + 266 \ \text{days}.
Formula (extracted LaTeX)
\[\mathrm{EDD} = \mathrm{Conception} + 266 \ \text{days}.\]
\mathrm{EDD} = \mathrm{Conception} + 266 \ \text{days}.
Formula (extracted LaTeX)
\[\mathrm{EDD} = D_s + (280 - GA_s)\ \text{days}.\]
\mathrm{EDD} = D_s + (280 - GA_s)\ \text{days}.
Formula (extracted text)
LMP method (Naegele’s rule, 28-day cycle): $ \mathrm{EDD} = \mathrm{LMP} + 280 \ \text{days} $ Adjusted for cycle length \(C\) (days): Ovulation \(= \mathrm{LMP} + (C - 14)\) days; then $ \mathrm{EDD} = \mathrm{Ovulation} + 266 \ \text{days}. $ Conception known: $ \mathrm{EDD} = \mathrm{Conception} + 266 \ \text{days}. $ IVF transfers: 3-day: \( \mathrm{EDD} = \mathrm{Transfer} + 263\ \text{days} \) ; 5-day: \( \mathrm{EDD} = \mathrm{Transfer} + 261\ \text{days} \). Ultrasound dating: Given scan date \(D_s\) and gestational age at scan \(GA_s\) (days), $ \mathrm{EDD} = D_s + (280 - GA_s)\ \text{days}. $
Variables and units
  • No variables provided in audit spec.
Sources (authoritative):
Changelog
Version: 0.1.0-draft
Last code update: 2026-01-19
0.1.0-draft · 2026-01-19
  • Initial audit spec draft generated from HTML extraction (review required).
  • Verify formulas match the calculator engine and convert any text-only formulas to LaTeX.
  • Confirm sources are authoritative and relevant to the calculator methodology.
Verified by Ugo Candido on 2026-01-19
Profile · LinkedIn
Formulas

(Formulas preserved from original page content, if present.)

Version 0.1.0-draft
Citations

Add authoritative sources relevant to this calculator (standards bodies, manuals, official docs).

Changelog
  • 0.1.0-draft — 2026-01-19: Initial draft (review required).