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Calculators

Pregnancy Due Date Calculator

Estimated due date from the first day of your last period.

Updates as you type
Nothing is sent anywhere

Your figures

Result

How to use this tool

  1. Enter your own figures over the defaults — First day of last period.
  2. The answer updates as you type. There is no button, and nothing is sent anywhere.
  3. Change one input at a time to see how sensitive the answer is to it.

Uses Naegele's rule — 280 days from the last menstrual period. It assumes a regular 28-day cycle, so an early scan gives a more reliable date.

How it works

This takes 1 input — first day of last period — and returns enter a date. The whole calculation happens in this page as you type: there is no submit button, no request, and nothing stored.

A worked example

Worked through with the figures the page already has in it: first day of last period of undefined, giving enter a date of —. These numbers come from running the calculator’s own code, not from being typed in here, so they cannot drift away from what you see on screen.

Starting from:

  • First day of last period: undefined
ResultValue
Enter a date—

Pregnancy Due Date Calculator — frequently asked questions

How accurate is a due date?

Only about 4% of babies arrive on the estimated date. Most births fall within two weeks either side.

What if my cycle is irregular?

The calculation assumes a 28-day cycle and ovulation on day 14. If yours differs, a dating scan is considerably more reliable.

Should I rely on this?

No. It is a rough guide. Your midwife or doctor will date the pregnancy properly with an ultrasound.

Is this calculator free?

Yes, with no account, no limits and no data collection. It runs entirely in your browser.

Should I rely on this for a financial or medical decision?

No. It is a planning estimate built on standard formulas and stated assumptions. For decisions that matter, speak to a qualified professional who can account for your full circumstances.

Is this calculator accurate?

The arithmetic is exact — it uses the standard formula. What limits accuracy is the assumptions: the figures you enter, and factors the formula does not model such as fees, taxes and rule changes.

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Background reading: Loan, Mortgage and Investment Calculators Explained

Nothing is sent anywhere. The figures you type stay in this page and are never transmitted or stored — how that works.

Disclaimer. The formula is exact; the answer is only as good as the figures and assumptions above. Not financial, tax, medical or legal advice. Full disclaimer.