HealthCalc Hub

Due date for conception in September

This page maps September dates to due dates. A conception on day 1 gives 25 May, and on day 30 it gives 23 June.

Pick a date to see your due date.

This calculator gives general information only. It is not medical advice. Talk to a doctor or other qualified health professional about your own health.

How it works

Add 266 days to the day of conception to get the due date. The table does this for each day of September. The September table has 30 rows, one per day.

Worked example

Start at 15 September. Count 266 days ahead to reach 8 June. Across the whole month the due dates run from 25 May to 23 June. This example assumes a 365-day year.

Estimated due date for each day of September, counting 266 days from the day of conception. The table uses a 365-day year.

Date of conceptionDue date
1 September25 May
2 September26 May
3 September27 May
4 September28 May
5 September29 May
6 September30 May
7 September31 May
8 September1 June
9 September2 June
10 September3 June
11 September4 June
12 September5 June
13 September6 June
14 September7 June
15 September8 June
16 September9 June
17 September10 June
18 September11 June
19 September12 June
20 September13 June
21 September14 June
22 September15 June
23 September16 June
24 September17 June
25 September18 June
26 September19 June
27 September20 June
28 September21 June
29 September22 June
30 September23 June

Common questions

What if I only know the month?

Use the middle of the month. The due date then falls in the middle of the window. Day 15 of September maps to 8 June.

How many weeks is the gap?

Divide the days by 7 to get weeks. From day 1 of September to 25 May is 266 days, which is 38 weeks.

What if my cycle is not regular?

When cycles are irregular, an ultrasound can date a pregnancy more reliably than a calendar. A date of 15 September would then give 8 June only as a first guess.

Does the year change the due date?

Only if the span includes 29 February, which moves the date one day earlier. If the span from 15 September includes a 29 February, 8 June reads one day earlier, as 7 June.

How reliable is a due date worked out by month?

It is an estimate, and births spread across the weeks around it. A conception on day 15 of September gives 8 June, with arrivals spread across the weeks around that date.