HealthCalc Hub

Due date for conception in December

If your conception is in December, your due date falls in August and September. Use the form for the exact day, or look it up in the table.

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 December. In December the due dates run through August and September.

Worked example

Take 15 December as the day of conception. 266 days later is 7 September. The first day of December lands on 24 August and the last lands on 23 September. The year in this example has 365 days.

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

Date of conceptionDue date
1 December24 August
2 December25 August
3 December26 August
4 December27 August
5 December28 August
6 December29 August
7 December30 August
8 December31 August
9 December1 September
10 December2 September
11 December3 September
12 December4 September
13 December5 September
14 December6 September
15 December7 September
16 December8 September
17 December9 September
18 December10 September
19 December11 September
20 December12 September
21 December13 September
22 December14 September
23 December15 September
24 December16 September
25 December17 September
26 December18 September
27 December19 September
28 December20 September
29 December21 September
30 December22 September
31 December23 September

Common questions

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 December would then give 7 September 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 December includes a 29 February, 7 September reads one day earlier, as 6 September.

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 December gives 7 September, with arrivals spread across the weeks around that date.

Which month will my baby be born?

The due date month is a guide, and many births come earlier or later. A conception in December points to August and September.

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 December maps to 7 September.