Pregnancy Due Date Calculator
Naegele-adjusted due date, gestational age, and days to go.
Pregnancy Due Date Calculator
Estimate your due date with Naegele's rule and see gestational age, trimester, and days remaining.
Day 1 is the first day of full bleeding, not the last day.
Cycles longer than 28 days push ovulation — and the due date — later.
Set a future date to see how far along you will be then.
Mon, 7 June 2027
2027-06-07
Gestational age
8 weeks 4 days
Trimester
1
Days remaining
220
Estimated conception
2026-09-14
That is 60 days since the first day of your last period.
This is an estimate based on calendar dates, not a medical diagnosis or a dating scan. Only about 4% of babies arrive on their estimated due date. Speak to your midwife, GP, or obstetrician about dating and any symptoms that worry you.
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What This Calculator Does
The Pregnancy Due Date Calculator estimates when your baby is due from the first day of your last menstrual period (LMP) or a known conception date. It applies Naegele's rule, adjusts for cycles that are not 28 days long, and reports gestational age, trimester, and the days remaining.
How It Works
An LMP-based estimate adds 280 days (40 weeks) to the first day of your last period, then shifts by the difference between your average cycle length and 28 days because a longer cycle ovulates later. A known conception date adds 266 days (38 weeks). Gestational age is counted from the LMP rather than conception, which is why you are considered about two weeks pregnant on the day of conception.
Example
An LMP of 1 January 2026 with a 28-day cycle gives an estimated due date of 8 October 2026. On 9 April 2026 that is 14 weeks 0 days, in the second trimester, with 182 days remaining. The same LMP with a 35-day cycle moves the estimate to 15 October 2026.
Formula
Due date = LMP + 280 days + (cycle length − 28)280 days is 40 weeks from the first day of the last period.
Due date = Conception + 266 days266 days is 38 weeks, because gestational age includes the two weeks before conception.
Weeks = floor((today − LMP) / 7), days = (today − LMP) mod 7Reading the Results
Estimated due date
The 40-week date calculated from your LMP or conception date. It is a midpoint, not an appointment: only about 4% of babies arrive on it.
Gestational age
Weeks and days since the first day of your last period — the convention used in antenatal care, scans, and test windows.
Estimated conception
The date of fertilisation implied by your dates, roughly two weeks after the LMP in a 28-day cycle.
Sources and References
ACOG Committee Opinion 700 — Methods for Estimating the Due Date
280 days from LMP; 266 days from conception
ACOG notes that an ultrasound before 14 weeks is the most accurate dating method and that the estimated due date should be revised when scan dating differs materially.
NICE NG201 — Antenatal care
Dating scan offered at 11–14 weeks
UK guidance uses the dating scan to confirm gestational age and the estimated due date.
References identify the method or data behind this calculator. Where a standard or tariff changes, the current edition applies, and the assumptions stated above take precedence over a remembered figure.
Frequently Asked Questions
How accurate is an estimated due date?
Only about 4% of births happen on the estimated date. Most arrive within two weeks either side, and first pregnancies often run a little later. An early ultrasound is more accurate than calendar dating, especially with irregular cycles.
Why does cycle length change the due date?
Naegele's rule assumes ovulation on day 14 of a 28-day cycle. If your cycles average 35 days, ovulation is about a week later, so the due date moves about a week later as well.
What if my ultrasound gives a different date?
Clinicians usually keep the scan date when it differs materially from the calendar estimate, particularly before 14 weeks. Ask your midwife or doctor which date they will use for your care.
Can I calculate a due date without knowing my last period?
Yes. If you know your conception or ovulation date, use the conception method, which adds 266 days. If you know neither, a dating scan is the reliable route.