How accurate is this?

It's a well-established estimate but only ~4% of babies are born on their calculated due date. Most arrive within two weeks either side. An early ultrasound gives a more accurate date.

My cycle isn't 28 days — does this still work?

Yes — enter your average cycle length and we shift the due date accordingly. If your cycles are very irregular, ask your provider for a dating scan.

Can I use a conception date instead?

For this tool, no — enter the first day of your last period. If you only know the conception date, subtract 14 days and use that as the LMP.

Is the Due Date calculator free?

Yes — free to use, with no signup, no limits and no personal details required. The site is supported by advertising rather than subscriptions.

Is my data saved or sent anywhere?

No. Every calculation runs in your browser, so the numbers you type are never transmitted to us or stored on a server. Closing the tab discards them.

Can I rely on this instead of seeing a professional?

No. These formulas give a useful reference point, but they cannot account for your medical history or body composition. Use the result to inform a conversation with a qualified professional, not to replace one.

Can I share or save my results?

Yes. Your inputs are stored in the page URL, so you can copy the link from the address bar (or use the share button) to bookmark a scenario or send it to someone else.

Pregnancy Due Date Calculator

Estimated due date, current week and trimester, based on your last menstrual period and cycle length.

Your details

First day of last period

Average cycle length

days

Estimated due date

Tuesday, 20 April 2027

You are currently

8w 4d

Trimester 1

Days until due

219

Pregnancy timeline (0 – 40 weeks)

1st trimester2nd trimester3rd trimester

Not medical advice. This is an estimate based on a standard 40-week pregnancy. Only around 4% of babies arrive on their exact due date. Your midwife or doctor will confirm gestational age via ultrasound.

How this is calculated

The most common estimate uses Naegele's rule: due date = first day of last menstrual period (LMP) + 280 days (40 weeks). Because ovulation happens roughly two weeks into a 28-day cycle, longer cycles push the due date later. We adjust by (cycle length − 28) days.

Gestational age is measured from the LMP, so at conception you're already considered ~2 weeks pregnant. Trimesters are commonly split as: 1st (weeks 0–12), 2nd (13–26), 3rd (27–40).

Who this calculator is for

This is aimed at people tracking their own health who want a clear number to work from rather than a vague guideline. It is useful as a starting reference point when setting goals or reviewing progress, and as context for a conversation with a qualified professional.

Assumptions and accuracy

These are population-level formulas. They do not account for body composition, muscle mass, pregnancy, medical conditions, or medication, so an individual result can be some way off. This is general information, not medical advice — speak to a doctor or registered dietitian before acting on it.

Frequently asked questions

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