Health & Wellbeing2 min check

Pregnancy Due Date Calculator

Estimate your due date using Naegele's rule (LMP + 280 days) or from a known conception date.

Short answer

From your last menstrual period (LMP), the standard estimated due date (EDD) is LMP + 280 days. Only ~5% of babies arrive on the exact date — most arrive within 2 weeks either side. A dating scan at 8–14 weeks is more accurate.

Step 1 of 10%

Calculation method, coverage and version

Inputs used: I know my…, Date (YYYY-MM-DD), Cycle length (days).
Calculation approach: The calculator applies the rules and assumptions described in “How it works” to the values you enter. Rounding can cause small differences from an official or provider calculation.
Coverage: Health & Wellbeing. UK nations, tax treatment, local rules and provider criteria can differ; check the official sources shown below before acting.
Content version: No page-specific review date is currently published. Treat the result as indicative and verify current rules independently.

Not included unless explicitly requested: personal circumstances not entered, provider discretion, future rule changes, professional fees and case-specific exceptions. Read the full calculator methodology.

How it works

Naegele's rule: due date = LMP + 280 days (40 weeks). For longer/shorter cycles, add or subtract the difference from 28 days. From a known conception date, due date = conception + 266 days (38 weeks).

Worked example

LMP: 1 January 2026, 28-day cycle.

EDD = 1 Jan + 280 days = 8 October 2026

Who should use this

•Newly pregnant women working out the EDD
•Partners and families counting weeks
•Anyone curious about trimester timing

Common mistakes

×Counting from conception assuming it's the same as LMP (it's ~14 days later)
×Forgetting cycle-length adjustments for irregular cycles
×Treating the EDD as a hard deadline — full term is 37-42 weeks
×Using LMP if you're unsure — a dating scan is more accurate

Frequently asked questions

How accurate is a due date?▾

Naegele's rule is ±2 weeks for most pregnancies. A first-trimester scan is accurate within ±5 days.

What if my cycle isn't 28 days?▾

Add (cycle - 28) days. So a 32-day cycle pushes the EDD by 4 days later.

When does each trimester start?▾

T1: weeks 1-12; T2: weeks 13-26; T3: weeks 27-40.

What if my baby is overdue?▾

Up to 42 weeks is normal. Most UK trusts offer induction discussion at 41 weeks.

Is conception the same as LMP?▾

No — conception is usually about 14 days after LMP in a 28-day cycle.

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