Calculate Your Due Date
Choose your preferred calculation method and get your estimated delivery date instantly.
Your Estimated Due Date
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How to Use This Calculator
Getting your estimated due date is straightforward. Start by selecting which calculation method works best for you. If you remember the first day of your last period, that’s the most common starting point. Just pick that date from the calendar and tell us your typical cycle length—most people have a 28-day cycle, but yours might be shorter or longer.
Know exactly when conception happened? Maybe you were tracking ovulation or had a fertility procedure. In that case, the conception date method will give you the most precise estimate. Just select that option and enter the date.
For those who conceived through IVF, we have a specialized calculator that accounts for whether you had a day 3 or day 5 embryo transfer. This method is incredibly accurate because we know the exact moment your pregnancy began.
If you’ve already had an ultrasound, you can use those measurements too. Enter the date of your scan and the gestational age your doctor gave you. Early ultrasounds are particularly reliable for dating pregnancies.
Why Accurate Dating Matters
Knowing your due date isn’t just about circling a day on the calendar. It helps your healthcare provider monitor your baby’s growth at each appointment. They’ll know what developmental milestones to look for and when to schedule important tests and screenings.
Your estimated delivery date also helps you plan maternity leave, prepare your home, and know when to pack that hospital bag. While only about 5% of babies arrive exactly on their due date, most show up within two weeks on either side of it.
How the Calculation Works
When you enter your last menstrual period, we add 280 days (40 weeks) to find your due date. This follows the standard method healthcare providers have used for generations. It assumes you ovulated about 14 days into your cycle, though we adjust for different cycle lengths.
For conception dates, we add 266 days instead, since we’re starting from fertilization rather than your period. IVF calculations are similar but account for the embryo’s age at transfer—either 3 or 5 days old.
Ultrasound dating works differently. We take the gestational age from your scan and calculate backward to figure out your conception date, then forward to your due date. First-trimester ultrasounds are the gold standard because all babies grow at roughly the same rate early on.
Frequently Asked Questions
Can my due date change after it’s calculated?
Yes, your due date might be adjusted based on ultrasound measurements, especially if there’s a significant difference from the date calculated by your last period. Healthcare providers often revise the due date if an early ultrasound shows the baby measuring differently than expected. First-trimester ultrasounds are considered more accurate than dates based on menstrual periods alone, particularly for women with irregular cycles.
What if my cycles are irregular?
Irregular cycles make it harder to predict ovulation, which means the last menstrual period method might not be as accurate for you. If your cycle varies by more than a few days each month, talk with your healthcare provider about getting an early ultrasound for dating. You might also have success if you were tracking ovulation and know your conception date.
How accurate is the due date for twins or multiples?
The calculation methods are the same for multiples, but twins and triplets typically arrive earlier than singletons. On average, twins are born around 35 weeks, and triplets around 32 weeks. Your healthcare provider will monitor you more closely and may have different expectations about your delivery timing.
What’s the difference between gestational age and fetal age?
Gestational age starts counting from your last menstrual period, while fetal age counts from conception—usually about 2 weeks later. When your doctor says you’re “10 weeks pregnant,” they mean 10 weeks of gestational age. Your baby’s actual age is probably closer to 8 weeks. We use gestational age because it’s easier to track consistently.
Why do so few babies arrive on their exact due date?
A “due date” is really a due week or even due month. Pregnancy length varies naturally between individuals, and many factors influence when labor starts. Anywhere from 37 to 42 weeks is considered full term. Your body and baby work together to determine the right time, which might not match our mathematical predictions.
Should I use ultrasound dating or LMP dating?
If you have an early ultrasound (before 13 weeks), that’s generally more reliable than counting from your last period, especially if your cycles are irregular or longer than 28 days. However, if your ultrasound date and LMP date are very close, your provider might stick with the LMP date. Different medical organizations have specific guidelines about when to prefer one method over another.
Calculation Method Comparison
Different situations call for different calculation methods. Here’s how they stack up:
| Method | Best For | Accuracy | Requirements |
|---|---|---|---|
| Last Menstrual Period | Regular cycles, known last period | Within 1-2 weeks | First day of last period, cycle length |
| Conception Date | Known ovulation, fertility tracking | Within 3-5 days | Exact or estimated conception date |
| IVF Transfer | IVF pregnancies | Highly precise | Transfer date and embryo age |
| Ultrasound | Irregular cycles, uncertain dates | Within 3-5 days (first trimester) | Scan date and gestational age |
What Affects Due Date Accuracy
Cycle Variability
Your menstrual cycle length plays a huge role in accuracy. The standard 28-day cycle assumes ovulation on day 14, but if you have a 32-day cycle, you probably ovulate around day 18 instead. That four-day difference shifts your due date. Women with very short cycles (under 25 days) or long cycles (over 35 days) often find that LMP-based calculations need adjustment.
Ovulation Timing
Not everyone ovulates exactly in the middle of their cycle. Stress, illness, hormonal changes, and dozens of other factors can shift ovulation earlier or later. This is why knowing your actual conception date—through ovulation tracking or fertility treatments—gives you more reliable results than just counting from your period.
First Ultrasound Timing
Ultrasounds are most accurate for dating when performed between 7 and 13 weeks. During this window, all babies grow at nearly identical rates, so measuring the baby tells us precisely how far along you are. Later ultrasounds are less useful for dating because babies start growing at individual rates—some bigger, some smaller, all perfectly healthy.
Individual Variation
Every pregnancy is unique. Some women consistently carry to 41 weeks, others tend to deliver at 38 weeks. Family history, your own birth timing, ethnicity, and whether it’s your first baby all play a role. This natural variation means the “due date” is really a best estimate, not a guarantee.
Common Misconceptions About Due Dates
Myth: Due dates are exact predictions
Many people think the due date is when the baby will definitely arrive, but it’s actually the middle of a probability range. Only about 5% of babies are born on their exact due date. Most arrive sometime during the four weeks centered around that date—two weeks before or two weeks after. Think of it as a target, not a deadline.
Myth: Later ultrasounds are more accurate
It seems logical that a more developed baby would be easier to measure accurately, but the opposite is true. First-trimester ultrasounds are far better for dating because early embryos all develop at the same pace. By the third trimester, genetic factors, nutrition, and placental function create huge variations in baby size, making it impossible to date the pregnancy accurately from measurements alone.
Myth: You can’t get pregnant during your period
While uncommon, it’s possible. Sperm can survive in your reproductive tract for up to five days. If you have a short cycle and ovulate early, sperm from period sex could still be around when you ovulate. This is one reason why the “rhythm method” has a high failure rate.
Myth: All pregnancies last exactly 40 weeks
Forty weeks is the average, but normal pregnancy length ranges from 37 to 42 weeks. First-time mothers often go a bit past 40 weeks, while women who’ve given birth before might deliver a few days earlier. Your body doesn’t follow a stopwatch.