Pregnancy Due Date Calculator

What this calculator does

If you've ever opened a spreadsheet just to answer one health & fitness question, this pregnancy due date calculator replaces the whole workbook: type the numbers, read the result.

Naegele's rule adds 280 days (40 weeks) to the last menstrual period.

Includes a copy-ready summary and printable PDF view.

Result updates live as you type — no "Calculate" button needed.

Inputs required: 1

Formula and worked example are shown in plain language below.

How to use the Pregnancy Due Date Calculator

Enter your values in the fields on the left.
Results update automatically.
Use the action buttons to copy, share or print.

The formula

Due date = LMP + 280 days

Worked example

LMP Jan 1 → Due date ~Oct 8.

Common mistakes

Irregular cycles reduce accuracy
Not accounting for conception date
Ignoring ultrasound updates

When to use it

Use as an estimate — ultrasound is more accurate.

Pro tips for the Pregnancy Due Date Calculator

Change one input at a time to see which lever actually moves the answer the most.
Round-trip check: reverse the inputs to confirm the formula matches what you'd compute by hand.
Bookmark this page: the URL and inputs are all you need to reproduce the exact result later.

Frequently asked questions

›Accuracy?

±2 weeks for most; ultrasound refines.

›Conception date?

Usually 2 weeks after LMP.

›Full-term?

37–42 weeks.

›IVF?

Use transfer date + specific rules.

›When to see doctor?

Positive test → book prenatal appointment.

›Can I use this on mobile?

Yes — the pregnancy due date calculator is fully responsive, and results, charts, and the share button all work on phones and tablets.

›How accurate is this pregnancy due date calculator?

The formulas match the standard textbook definition shown above. Rounding is applied only for display; underlying computation uses full floating-point precision. For regulated health & fitness decisions, always confirm with a qualified professional.

Embed this calculator

Drop the Pregnancy Due Date Calculator into your own site or blog post. Free to use — a small “Powered by CalcPilot” link is appreciated.

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