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Current week
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.
Please enter a valid LMP date. Cycle length should be between 21 and 45 days.
Estimated due date
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Trimester
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Days remaining
How to Use the Pregnancy 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.
Pick the first day of your last period. Leave the cycle length at 28 days, or change it to your usual length (21 to 45 days are accepted). The result shows the estimated due date, the current week, the trimester and the days remaining. The week, trimester and days remaining are counted from today’s date, so they change each day.
Pregnancy 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 calculator adds 280 days to the first day of the last period, then adds or subtracts the difference between your cycle and 28 days. The week is the number of whole weeks since that date, and it shows 0 if the date is in the future. Weeks 0 to 12 are the first trimester, 13 to 26 the second and 27 onwards the third. Days remaining counts down to the due date and goes negative after it. It does not use ultrasound, conception or IVF dates.
Pregnancy 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.
Worked example: first day of last period 1 March 2026 with a 28-day cycle gives Sunday, December 6, 2026. With a 32-day cycle the due date moves to Thursday, December 10, 2026, and with a 24-day cycle to Wednesday, December 2, 2026. If you calculate on 3 October 2026 with the 28-day cycle, the result shows Week 30, 3rd trimester and 64 days remaining.
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 your local care pathway.
Key Features & Benefits of This Pregnancy Due Date Calculator
- Naegele’s rule with cycle adjustment — the due date is the first day of your last period plus 280 days, shifted for cycles that are not 28 days long (21 to 45 days accepted).
- Due date, week, trimester and days remaining — all four appear in one result.
- Counts from today — the current week, trimester and days remaining change each day.
- A planning aid, not a medical date — ultrasound, conception and IVF dates are not used, so confirm your date with a healthcare provider.
- Instant, free and private — runs entirely in your browser, no sign-up, nothing stored.
Good to know
Antenatal schedules differ from country to country. Treat the estimated date as a planning aid and follow the visit timeline provided by your local maternity service.
Pregnancy 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.
Sources and review
Sources last checked: . These sources give the background for this calculator. They are general information and do not replace advice from your doctor or midwife.
- NHS: Pregnancy due date calculator: pregnancy normally lasts 37 to 42 weeks from the first day of your last period, and the 12-week scan can estimate how far along you are more accurately.