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Due date calculator

Just got a positive pregnancy test? One of your first questions is probably: "When is my baby due?" Use Lively's pregnancy due date calculator to estimate when you'll meet your little one.

Your data stays on your device

Lively does not collect, process, or store the values you enter. All calculations happen locally in your browser.

How is my due date calculated?

Pregnancy due dates are calculated by adding 40 weeks (280 days) to the first day of your last menstrual period (LMP). This method is used because pinpointing the exact conception date is difficult, sperm can survive up to 5 days, and ovulation timing varies.

Here's how it works

  • 1Start with the first day of your last period
  • 2Add 40 weeks (280 days)
  • 3That's your estimated due date!

Example: If your last period started on January 1, your estimated due date would be around October 8.

This calculation assumes a typical 28-day cycle with ovulation around day 14. If your cycle is shorter or longer than 28 days, your actual due date may differ. That's why an ultrasound confirmation with your doctor is essential.

When will my baby arrive? Quick reference

Wondering what month you might be due? Here's a quick guide based on conception month (assuming a 40-week pregnancy):

Conceived in January → Due in October
Conceived in February → Due in November
Conceived in March → Due in December
Conceived in April → Due in January
Conceived in May → Due in February
Conceived in June → Due in March
Conceived in July → Due in April
Conceived in August → Due in May
Conceived in September → Due in June
Conceived in October → Due in July
Conceived in November → Due in August
Conceived in December → Due in September

Remember, very few babies actually arrive on their due date! It's completely normal to give birth anywhere between 37 and 42 weeks of pregnancy.

How accurate is a pregnancy due date?

Here's the truth: Due dates are educated estimates, not guarantees. Only about 5% of babies arrive exactly on their due date. Most babies are born between 37 and 42 weeks of pregnancy, that's a 5-week window!

Think of your due date as a target month rather than a specific day. The Lively app helps you track your pregnancy week by week, so you'll know what to expect no matter when your baby decides to arrive.

Why your due date matters for prenatal care

While your due date is an estimate, it plays an important role in your prenatal care. Your healthcare provider uses it to:

  • Schedule important tests and screenings at the right time
  • Monitor your baby's growth and development appropriately
  • Determine if your pregnancy is full-term, preterm, or post-term
  • Plan timing for induction if needed
  • Track milestones throughout your pregnancy journey

Knowing your gestational age helps ensure you and your baby get the right care at the right time. Use the Lively app to follow your baby's development week by week and get personalized tips for each stage of pregnancy.

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Frequently asked questions

Add 40 weeks (or 280 days) to the first day of your last menstrual period. This gives you an estimated due date based on a typical 28-day cycle. For a quick calculation, use Lively's pregnancy due date calculator above. Remember to confirm with your healthcare provider.

If you have irregular periods, calculating due dates from your last period is less accurate. Your doctor will likely use an early ultrasound to measure your baby and determine a more precise due date. The ultrasound method is the most reliable for people with irregular cycles.

If you don't remember when your last period started, don't worry. Your healthcare provider can estimate your due date using an ultrasound, which measures your baby's size. This is often more accurate anyway, especially in early pregnancy. Start tracking your cycles with Lively for future reference.

Due date calculators provide helpful estimates but aren't 100% accurate. They assume a 28-day cycle and ovulation on day 14, which doesn't apply to everyone. Ultrasound dating, especially in the first trimester, is the most accurate method. Only about 5% of babies are born on their exact due date.

Your estimated due date may be adjusted after your first ultrasound if the measurements suggest a different gestational age. However, once confirmed by ultrasound, your due date typically won't change unless there's a clear reason. Even so, remember that babies rarely arrive exactly on schedule.

Gestational age is measured from the first day of your last period (what doctors use), while fetal age is measured from conception, which is typically about 2 weeks later. When someone says you're "8 weeks pregnant," they're referring to gestational age, your baby's actual age is closer to 6 weeks.

For the most accurate results, take a pregnancy test on the first day of your missed period or a few days after. Testing too early can result in a false negative because hCG levels haven't built up enough yet. Use Lively's pregnancy test calculator to find your optimal testing window.

To calculate how far along you are, count the number of weeks from the first day of your last period. For example, if your last period started 6 weeks ago, you're 6 weeks pregnant. Use Lively's pregnancy calculator or app to track your progress week by week with personalized insights.

Important notice

This calculator is provided for informational and educational purposes only. It is not intended to diagnose, treat, cure, or prevent any medical condition, nor is it a substitute for professional medical advice, diagnosis, or treatment.

Always consult with a qualified healthcare provider before making any health-related decisions or if you have questions about your health. Never disregard professional medical advice or delay seeking it because of information provided by this tool.

Your use of this calculator is at your own risk. Results are estimates based on general guidelines and may not reflect your individual circumstances.