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Pregnancy Due Date Calculator

Enter your values below to get the result first, then scroll for the full explanation and guidance.

Step 1 • Add values

Use the calculator

Enter your values below to generate an instant result. You can update the inputs at any time to compare different scenarios.

Example: an LMP of 29 February 2024 and a 28-day cycle gives an estimated due date of 5 December 2024.

Results refresh instantly as values change.

Estimated due date

22 October 2026LMP and cycle-length estimate

Estimated due date: 22 October 2026 (LMP and cycle-length estimate)

This gives a planning estimate only. Obstetric dating can change after scans or clinical review.

Pregnancy timing summary

This gives a planning estimate only. Obstetric dating can change after scans or clinical review.

Result snapshot

A quick visual read of the values behind this result.

First day of last period15 January 2026
Cycle length28 days
Current pregnancy age13 weeks 5 days

Recommended next checks

  • →Use the pregnancy calculator if you want estimated weeks and days from the same information.
  • →A dating scan can revise this estimate; use your maternity team's date if one has been provided.
First day of last period
15 January 2026
Cycle length
28 days
Current pregnancy age
13 weeks 5 days

Try different values to compare results.

This calculator follows the NHS LMP-and-cycle-length approach to estimate when a baby might arrive. The result is an estimated due date only and may change after a dating scan or clinical review.

Fast to use

Built for comparison

Clear result output

Table of Contents

5

About Pregnancy Due Date Calculator

Pregnancy Due Date Calculator helps you work through the main numbers for this topic quickly with a simple input flow and an instant result.

Use the calculator result as a practical starting point, then review the explanation and assumptions on the page if you want more context.

Estimated due date, not a fixed delivery date

For a 28-day cycle, the estimate adds 280 days to the first day of the last menstrual period. Each day above or below 28 shifts the estimate by one day. Leap-year date arithmetic is handled as calendar days.

NHS guidance notes that pregnancy normally lasts from 37 to 42 weeks from the first day of the last period and that a 12-week scan can date the pregnancy more accurately. Assisted-conception dates require a separate clinically supported method and are not accepted here.

Formula explained

Calculation flow

This calculator is structured for fast UK-focused estimates with clear inputs, repeatable logic, and instant results.

Formula

Input values -> calculation engine -> instant result

How the result is built

1Enter the values requested in the form.
2The calculator applies the configured formula logic.
3The result updates instantly with a breakdown.
4Use the output to compare scenarios quickly.

Example

Example: an LMP of 29 February 2024 and a 28-day cycle gives an estimated due date of 5 December 2024.

Assumptions

  • Estimated due date = first day of LMP + 280 days + (regular cycle length - 28 days).
  • Supports regular 21-to-35-day cycles and a current date within the estimated 0-to-42-week gestational window.
  • Does not model conception dates, embryo transfers, irregular cycles, uncertain LMP or ultrasound measurements.

Source basis

  • UK-focused calculator flow
  • Structured input validation
  • Instant result breakdowns

Trust and notes

Assumptions and important notes

This calculator is designed to give a fast estimate using the method shown on the page. Results are most useful when your inputs are accurate and the tool matches your situation.

Use the result as guidance rather than a final diagnosis or professional decision. If the result could affect health, legal, financial, or compliance decisions, verify it with a qualified source where appropriate.

  • Estimated due date = first day of LMP + 280 days + (regular cycle length - 28 days).
  • Supports regular 21-to-35-day cycles and a current date within the estimated 0-to-42-week gestational window.
  • Does not model conception dates, embryo transfers, irregular cycles, uncertain LMP or ultrasound measurements.

Method

UK calculator guidance

Last reviewed

April 17, 2026