Pregnancy Due Date Calculator

Written byOleh Soloninupdated 5 October 2026

How to count

First day of last period

Cycle length, days

Advanced options

Gestational age on

Leave empty for today.

Result

Estimated due date2026-10-22, Thursday
Gestational age37 weeks 5 days
Trimester3
Days to due date16
Weeks 37 to 412026-10-01 — 2026-11-04 (weeks 37–41)
Conceptionaround 2026-01-29

This result is informational only and is not professional advice.

Naegele's rule, with a correction for cycles that are not 28 days

Estimate a due date from the first day of your last period, adjusted for cycle length, plus how many weeks along you are today.

The standard method counts 280 days from the first day of the last period. It assumes a 28-day cycle with ovulation on day 14, so a longer or shorter cycle shifts the date accordingly.

Treat the result as a midpoint, not an appointment. Babies rarely arrive on the estimated date, and a dating ultrasound in the first trimester is considerably more accurate than any calendar calculation.

How to use

Choose what to count from: the first day of your last period, the conception date or the gestational age from a scan.
Enter the date. For a period, add your cycle length; for a scan, the scan date and the age it gave in weeks and days.
Read off the due date, how far along you are today, the trimester and the range of dates from week 37 to week 41.

How the due date is counted

Pregnancy is dated from the first day of the last period, and birth is expected on day 280 — 40 weeks. The calculator adds exactly 280 days, corrected for cycle length: a last period on 15 January gives a due date of 22 October. Naegele's 'nine months and seven days' is a calendar shortcut for the same count and can land a day or two away from it: from 1 March 2026, 280 days reach 6 December, while nine months and seven days reach 8 December.

If the conception date is known, the pregnancy is taken to start 14 days earlier, so the due date is 266 days after conception. If a scan gave the gestational age, the date is counted from that: 12 weeks 1 day on 10 April gives the same 22 October.

The American College of Obstetricians and Gynecologists (ACOG, Committee Opinion 700) treats an ultrasound before 14 weeks as the most accurate way to date a pregnancy. If that scan differs from the period date by more than 7 days, the due date is moved to match the scan; a smaller gap is left to the clinician, depending on how early the scan was done, and later changes are kept for rare cases.

A 28-day cycle. Every row comes from the calculator on this page.
First day of last period	Estimated due date
1 January 2026	8 October 2026
15 January 2026	22 October 2026
1 February 2026	8 November 2026
1 March 2026	6 December 2026
1 April 2026	6 January 2027
1 May 2026	5 February 2027

Cycle length moves the date

Naegele's rule assumes a 28-day cycle with ovulation 14 days after the period starts. A longer cycle means later ovulation, so the due date moves by exactly as many days as the cycle is longer than 28; a shorter cycle moves it earlier.

Last period on 15 January 2026. Every row comes from the calculator on this page.
Cycle length, days	Likely conception	Estimated due date
24	25 January	18 October
26	27 January	20 October
28	29 January	22 October
30	31 January	24 October
32	2 February	26 October
35	5 February	29 October

What this calculator shows

The estimated due date
Gestational age today in weeks and days
Which trimester that falls in and how many days remain

What to keep in mind

Counts 280 days from the last period, adjusted by the difference between your cycle and 28 days.
This is an estimate for planning. Antenatal care and ultrasound dating come from your clinician, not from a web page.

Where the numbers come from

Checked against Naegele's rule.

FAQs

How accurate is a due date?

It is a midpoint, not an appointment. A birth counts as term anywhere from 37 weeks 0 days to 41 weeks 6 days — a five-week window — and the due date is simply 40 weeks exactly.

Why count from the last period rather than conception?

Because the date of the last period is usually known and the date of conception rarely is. It means the first two weeks of a pregnancy counted this way happen before conception. If you know the conception date, count from that instead.

What if my cycle is not 28 days?

Enter your real cycle length. With a 32-day cycle ovulation comes later and the due date moves four days — from 22 to 26 October for a last period on 15 January.

When do the second and third trimesters start?

The first trimester runs to 13 weeks 6 days, the second from 14 weeks 0 days to 27 weeks 6 days, and the third starts at 28 weeks. For a last period on 15 January the second trimester begins on 23 April and the third on 30 July.

Which dates count as a term birth?

From 37 weeks 0 days to 41 weeks 6 days — the calculator shows that range. ACOG splits it into early term (weeks 37–38), full term (39–40) and late term (41). For a last period on 15 January it runs from 1 October to 4 November.

Should I rely on this instead of a scan?

No. A first-trimester ultrasound measures the fetus directly and is more accurate, especially with irregular cycles. Use this for a rough idea between appointments.

Worked example

A standard cycle

Input: Last period 15 January, 28-day cycle

Output: Due date around 22 October

Note: With a 32-day cycle the same start date moves the estimate four days later, since ovulation happens later in the cycle.

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Result

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