Curious about how a pregnancy due date calculator works or how doctors estimate when your baby
might arrive? Let’s break it down with insights from Dr. Sara Two good, an OB-GYN at Cedars-Sinai
Medical Group in California. Most healthcare providers estimate your due date based on your menstrual cycle or conception data. If you’re using a period-tracking app, you’ll have the first day of your last menstrual period (LMP) handy—making it easier to calculate your pregnancy timeline.
Depending on your conception method or cycle, doctors may use different ways to estimate your baby’s arrival.
If your cycle is regular and you were actively trying to conceive, you might have an idea of when conception occurred. However, due to the variability of ovulation and fertilization, this isn’t always the most accurate way to calculate pregnancy due date.
If you’ve undergone IVF, your pregnancy due date calculator becomes even more precise. Doctors calculate your estimated due date based on your IVF transfer date, knowing exactly when the embryo was transferred—typically a 3-day or 5-day transfer. Use Lunara’s IVF due date calculator to get a tailored estimate.
Ultrasound scans, especially in early pregnancy, can also help confirm or adjust your due date. This is particularly helpful for those with irregular cycles. The ultrasound measures your baby’s size to determine gestational age and ensure your pregnancy week calculator by due date remains accurate.
The most common method to calculate my due date starts with the first day of your LMP. Even though conception doesn’t occur on that exact day, it’s a reliable reference point since ovulation and fertilization can be tricky to pinpoint. Sperm can survive for up to five days, and your ovulation may not happen on the same day every cycle.
Step 1: Start with the first day of your last period
Step 2: Add 280 days (or 40 weeks) for your estimated due date
For example, if your period started on January 1, your estimated due date would be around October
8. It’s a straightforward way to calculate my pregnancy due date—but it assumes a 28-day cycle.
Since cycle lengths vary, this method may not be 100% accurate for everyone.
Conceived in January? Due in October
Conceived in February? Due in November and so on