HealthCalc Hub

Due date for a last period in March

Enter your last period start date to get a due date. This page is set up for March. The table below covers each day from day 1 to day 31.

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

Count 280 days forward from the first day of the last period. The result is the estimated due date. For March, day 31 maps to 5 January.

Worked example

Start at 15 March. Count 280 days ahead to reach 20 December. Across the whole month the due dates run from 6 December to 5 January. This example assumes a 365-day year.

Estimated due date for each day of March, counting 280 days from the first day of the last period. The table uses a 365-day year.

First day of last periodDue date
1 March6 December
2 March7 December
3 March8 December
4 March9 December
5 March10 December
6 March11 December
7 March12 December
8 March13 December
9 March14 December
10 March15 December
11 March16 December
12 March17 December
13 March18 December
14 March19 December
15 March20 December
16 March21 December
17 March22 December
18 March23 December
19 March24 December
20 March25 December
21 March26 December
22 March27 December
23 March28 December
24 March29 December
25 March30 December
26 March31 December
27 March1 January
28 March2 January
29 March3 January
30 March4 January
31 March5 January

Common questions

Does the year change the due date?

Only if the span includes 29 February, which moves the date one day earlier. The span from 15 March does not cross February. A leap year changes nothing for 20 December.

How reliable is a due date worked out by month?

It is an estimate, and births spread across the weeks around it. A last period on day 15 of March gives 20 December, 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 last period in March points to December and January.

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 March maps to 20 December.

How many weeks is the gap?

Divide the days by 7 to get weeks. From day 1 of March to 6 December is 280 days, which is 40 weeks.