Understanding Your Due Date: What It Really Means

So you just found out you're pregnant — congratulations! And someone just told you your due date. But here's the thing: that date is more of a guess than a guarantee.

What Is a Due Date?

Your due date is calculated by counting 40 weeks (280 days) from the first day of your last period. This is called the LMP method, and doctors have been using it forever.

The problem? This assumes you ovulate on day 14 of a 28-day cycle. Real life isn't that neat. Some people have longer cycles, shorter cycles, or irregular cycles. And even if your cycles are regular, ovulation can happen on different days in different months.

Only 1 in 20 Babies Show Up on Time

Here's a fun fact: only about 5% of babies are actually born on their due date. Some come two weeks early, some two weeks late. That "due month" is really more of a four-week window.

Why Your Due Date Might Change

During your first ultrasound (usually between 8-14 weeks), your doctor will measure your baby and give you a new estimated due date. This is actually more accurate than the LMP method, especially if:

• Your periods were irregular before pregnancy
• You got pregnant right after stopping birth control
• You don't remember your last period date
• Your cycles are longer or shorter than 28 days

If there's more than a week difference between your LMP due date and the ultrasound due date, your doctor will usually adjust it. That's totally normal.

The Bottom Line

Your due date is a helpful target, not a deadline. Think of it like a weather forecast — it gives you an idea of what to expect, but things change.

Use our calculator to get a ballpark estimate, then confirm with your OB at your first appointment. They'll give you the most accurate date based on your situation.