WorldCalcs

Due Date Calculator

Estimate your pregnancy due date from your last menstrual period (LMP) using Naegele's rule.

Reviewed by the WorldCalcs team · Methodology · Last reviewed: June 2026

Estimated due date

8 October 2026

Gestational age: 29 weeks 3 days · 3rd trimester

This is a general estimate, not medical advice. Only about 1 in 20 babies arrive on the due date — your doctor or midwife gives the most accurate dating. See our Disclaimer.

What is a due date calculator?

A due date calculator estimates when your baby is likely to arrive, based on the first day of your last menstrual period (LMP). A typical pregnancy lasts about 40 weeks (280 days) from that date. This tool gives your estimated due date plus how far along you are, and lets you adjust for a cycle longer or shorter than the usual 28 days.

How it's calculated

The standard method is Naegele's rule: add 280 days (40 weeks) to the first day of your last period. Because ovulation timing shifts with cycle length, the tool adjusts by the difference between your cycle and 28 days. Gestational age is then counted in weeks from the LMP. Only a small share of babies arrive exactly on the due date; it is a midpoint, not a deadline.

Example

For a last period starting 1 January 2026 with a typical 28-day cycle, the estimated due date is 280 days later: 8 October 2026. With a longer 35-day cycle, the tool adds 7 days, giving 15 October 2026.

All calculations happen in your browser. Nothing is sent, stored, or tracked.

Results are estimates and may contain errors — for general information only, not professional advice. Always verify before relying on them. Disclaimer

How to use

Enter the first day of your last menstrual period and, if you know it, your average cycle length. The tool returns the estimated due date, current gestational age and trimester.

This estimate is informational only. An early ultrasound or your clinician's assessment is more accurate.

Frequently asked questions

How is a due date calculated?+

By Naegele's rule: 280 days (40 weeks) from the first day of your last period.

How accurate is a due date?+

It is an estimate; only about 1 in 20 births happen exactly on the due date, and most arrive within two weeks either side.

What if my cycle isn't 28 days?+

The tool adjusts by the difference between your cycle length and 28 days, since that shifts when ovulation and conception occur.

What is the LMP?+

The first day of your last menstrual period, the standard starting point for dating a pregnancy.

How many weeks is full term?+

About 40 weeks from the LMP; 37 to 42 weeks is generally considered full term.

Can an ultrasound change my due date?+

Yes; early ultrasound dating is often more accurate and your provider may adjust the date.

How do I find my likely conception date?+

Roughly two weeks after the LMP in a 28-day cycle; see our Ovulation Calculator.

Is this a substitute for medical care?+

No; always confirm dates and care with your doctor or midwife.

References

  • Naegele's rule — estimated due date is about 280 days (40 weeks) from the first day of the last menstrual period (standard obstetric method).

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