Pregnancy Due Date Calculator

What this due date calculator does

It estimates your baby's expected due date from whichever piece of information you actually have — the first day of your last period, a known conception date, an IVF embryo transfer date, an ultrasound dating scan, or even a due date you were already given (to work backward and find the equivalent conception date). Along with the due date, it shows your current gestational age, trimester, and a full list of key milestone dates.

Who it's for

Anyone newly pregnant wanting a due date estimate before a first prenatal appointment, people going through IVF who want a due date based on their transfer date, and anyone who wants to double-check a due date a provider already gave them.

How to use it

• Pick which piece of information you have from the dropdown: last period, conception date, IVF transfer date, ultrasound dating, or an already-known due date.
• Fill in the date (and, for LMP, your average cycle length — the default of 28 days works for most people, adjust it if yours runs shorter or longer).
• Your estimated due date, current gestational age, and trimester appear instantly, along with a table of key pregnancy milestones mapped to actual calendar dates.

Real-world use cases

• Early pregnancy: get a due date estimate right after a positive test, before your first ultrasound confirms (or adjusts) it.
• IVF pregnancies: transfer-date-based due dates are typically more precise than LMP-based ones since the exact age of the embryo at transfer is known.
• Cross-checking a provider's due date: enter the due date you were given to see the equivalent LMP and conception date, useful for filling out other forms that ask for one or the other.
• Planning around milestones: see the actual calendar date for viability, full term, or the end of the first trimester instead of just counting weeks in your head.

Frequently asked questions

How is a due date calculated from the last period?

The standard method (Naegele's rule) adds 280 days — 40 weeks — to the first day of your last menstrual period, assuming a 28-day cycle with ovulation around day 14. This calculator adjusts that automatically if your average cycle is longer or shorter than 28 days.

Is the IVF transfer date more accurate than LMP dating?

Generally yes — since the embryo's exact age at transfer is known precisely (day 3 or day 5), the due date calculated from a transfer date tends to be more reliable than one estimated from a last period date, which depends on assumptions about cycle length and ovulation timing.

Why would my due date change after an ultrasound?

Early ultrasound measurements (particularly in the first trimester) are considered the most accurate way to date a pregnancy, sometimes more accurate than LMP-based dating if your cycle is irregular — that's why a provider may adjust your due date after a dating scan.

What's the difference between full term and early term?

"Early term" is 37–38 weeks, "full term" is 39–40 weeks, and "late term" is 41 weeks — research shows babies born in the full-term window tend to have the best outcomes, which is why providers avoid scheduling early inductions or C-sections before 39 weeks without a medical reason.

Do only about 1 in 20 babies arrive exactly on their due date?

Yes — a due date is a statistical estimate, not a prediction. Most babies are born within about a week and a half on either side of the calculated due date, so treat it as the middle of a range rather than an exact appointment.