Pregnancy Due Date Calculator

Knowing an estimated due date helps with appointment scheduling and milestone tracking. This due date calculator applies Naegele’s rule to the first day of the last menstrual period and adjusts for cycle length when it differs from 28 days. It also reports current gestational week, trimester and remaining days. The result is an estimate only; ultrasound dating and clinical judgement refine the official date. Figures and examples are oriented toward European users, with euro amounts and metric units where relevant.

First day of last period (LMP)

Average cycle length (days)

Please enter a valid LMP date. Cycle length should be between 21 and 45 days.

Estimated due date

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Current week

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Trimester

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Days remaining

How to Use the Due Date Calculator

Enter the first day of your last menstrual period (LMP).
Adjust average cycle length if it is not 28 days.
Calculate to see estimated due date, current week and trimester.
Discuss the result with a healthcare provider for confirmation.

Start with the inputs shown in the calculator and use the units or options that match your situation. Enter realistic values rather than estimates when you have the exact figures available. After you select Calculate, check the displayed result and the supporting breakdown. If you change an input, run the calculation again so the result reflects the updated assumptions. The tool is designed to make the process quick while keeping the underlying steps understandable.

Due Date Calculator Formula Explained

Naegele’s Rule with Cycle Adjustment

Standard Naegele’s rule: due date = LMP + 280 days (40 weeks). If average cycle length is C days, add (C − 28) days to the 280-day offset. Gestational age in weeks is the number of whole weeks from LMP to today. Trimesters are commonly grouped as weeks 1–12, 13–26 and 27–40+. Only a minority of births occur on the exact estimated date.

The displayed result depends on the inputs you provide and the calculation method described on this page. Keeping the inputs consistent with the stated units is important because changing a unit, period, rate, date, or percentage can change the result significantly. The calculator performs the arithmetic automatically, while the explanation gives you enough context to understand what is being combined, converted, or compared. For estimates, treat the output as an indication based on your assumptions rather than as a guaranteed real-world outcome.

Due Date Calculator Example Calculation

If the first day of the last menstrual period was 1 March and cycles are about 28 days, Naegele’s rule places the estimated due date around early December. Cycle lengths other than 28 days shift that estimate. Only a minority of births occur on the exact date—ultrasound dating may refine it.

This example is meant to show the order of the inputs and the way the final result is reached. In your own calculation, replace the example figures with your actual values and keep the same units throughout. A useful check is to change one input slightly and confirm that the result changes in a sensible direction. That simple check can help catch an incorrect unit, percentage, date, or other assumption before you rely on the result.

When to use this tool

Use this for a standard planning estimate of due date, week and trimester. Confirm all dates with your midwife or obstetric team under local European care pathways.

Key Features & Benefits of This Due Date Calculator

Built for real use — Use this for a standard planning estimate of due date, week and trimester.
Instant, free and private — runs entirely in your browser, no sign-up, nothing stored.
Formula-accurate — Naegele’s Rule with Cycle Adjustment Standard Naegele’s rule: due date = LMP + 280 days (40 weeks).
Works on any device — mobile or desktop, no app or installation needed.

Good to know

National antenatal schedules differ across Europe. Treat the estimated date as a planning aid and follow the visit timeline provided by your local maternity service.

Due Date Calculator — FAQs

How accurate is an LMP-based due date?

It is a population average. Cycle irregularity, uncertain LMP and early ultrasound measurements often shift the official date by several days.

What if I conceived through IVF?

IVF dating usually starts from transfer or retrieval date and is more precise; use a specialised IVF due-date method when that information is available.

Is this medical advice?

No. It is an informational estimate. Always follow guidance from your obstetric care provider.

How accurate is the LMP method?

It's a standard estimate accurate to within about two weeks for most pregnancies; an early ultrasound typically refines the date further.

The FAQs below address common questions about using this Pregnancy Due Date Calculator. They also explain assumptions and situations where the result may need additional context. If your situation uses a different rule, local rate, institutional policy, or professional standard, use the relevant source alongside the calculator rather than treating a general estimate as a definitive answer.