Calculating your due date
Your baby’s development actually takes 10 lunar months. (Although generally, people always talk of a ‘nine-month’ pregnancy) A lunar month consists of exactly 28 days.
A full-term pregnancy, therefore, lasts for 40 weeks (280 days) from the first day of the last menstrual period (LMP). However, this calculation assumes a cycle length of 28 days. If your cycle is not 28 days, you will have to calculate from an adjusted LMP date, that is, an LMP date adjusted as if you did have a 28-day cycle.
(This calendar, thank goodness, does this calculation for you automatically).
But, if you really enjoy figures, and you want to check, you can calculate your own adjusted LMP.
The LMP date + (Your cycle length - 28) = Your adjusted LMP date.
Example:
If your LMP is August 22, with a cycle of say, 32 days
Your adjusted LMP will be 26 August. Why?
Because (32 – 28 = 4 days) & 22 + 4 = 26 August. Easy!
Or:
If your LMP is 22 August with a cycle length of 24 days this time.
The adjusted LMP will be 18 August. (24 – 28 = minus 4 days) Get it?
This LMP adjustment will allow you to calculate your own due date using the standard tools. Alternatively, you can calculate your due date using the standard tools, and then adjust your due date as described below.
How "far along" you are can be calculated in two ways:
- From the date of your LMP;
OR - From the date of conception, which typically occurs two weeks after your LMP, which is called weeks from gestation.
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