Due Date Calculator 📅
Calculate your estimated due date and track your pregnancy milestones based on your last menstrual period.
Medical Disclaimer
The calculators and information on ParentCalc.com are for educational purposes only and should not replace professional medical advice. Always consult with your pediatrician or healthcare provider about your child's specific needs.
About the Due Date Calculator
The Due Date Calculator is an essential tool for expecting parents to estimate when their baby will arrive. Based on the proven Naegele's Rule, this calculator adds 280 days (40 weeks) to the first day of your last menstrual period (LMP) to determine your estimated due date. This method has been used by healthcare providers for decades and provides a reliable starting point for pregnancy planning.
Understanding your due date helps you prepare for your baby's arrival, schedule important prenatal appointments, plan maternity leave, and track your pregnancy milestones week by week. While only about 5% of babies are born on their exact due date, knowing this date gives you a two-week window when labor is most likely to begin naturally.
Our calculator also accounts for variations in menstrual cycle length, making it more accurate than standard calculators that assume a 28-day cycle. Whether you have a shorter or longer cycle, you'll get a personalized due date that reflects your unique situation.
How to Use This Calculator
- 1.Enter Your Last Menstrual Period (LMP): Input the first day of your last period. This should be the day your menstrual bleeding started, not when it ended. If you're unsure, check your calendar or period tracking app.
- 2.Select Your Average Cycle Length: Choose how many days typically pass between the first day of one period and the first day of the next. The average is 28 days, but anywhere from 21-35 days is normal.
- 3.Click Calculate: The calculator will instantly show your estimated due date, current week of pregnancy, trimester, and upcoming milestones.
- 4.Review Your Results: Save or screenshot your due date for future reference. Remember, this is an estimate that your healthcare provider may adjust based on ultrasound measurements.
Frequently Asked Questions
How accurate is the due date calculator?
Due date calculators are approximately 80% accurate within a two-week window. The calculation assumes a regular menstrual cycle and typical ovulation timing. Your healthcare provider may adjust your due date based on early ultrasound measurements, which can be more accurate, especially if done between 8-13 weeks of pregnancy.
What if I don't know the exact date of my last period?
If you're unsure of your exact LMP date, try to estimate within a few days. You can also wait for your first ultrasound, which can date your pregnancy accurately. Dating ultrasounds performed in the first trimester (before 14 weeks) are accurate within 5-7 days. If you have irregular periods or don't remember your LMP at all, an ultrasound will be the best way to determine your due date.
Can I calculate my due date if I know my conception date?
Yes! If you know your exact conception date (common with IVF or if you were tracking ovulation), you can calculate your due date by adding 266 days (38 weeks) to that date. This is actually more accurate than using LMP, as it doesn't rely on assumptions about when you ovulated. For IVF pregnancies, add 266 days to the egg retrieval date or 263 days to the transfer date for a 3-day embryo (or 261 days for a 5-day embryo).
Why did my doctor change my due date after an ultrasound?
Doctors often adjust due dates after early ultrasounds because fetal measurements in the first trimester are very consistent across all pregnancies. If the ultrasound shows your baby measuring larger or smaller than expected based on your LMP, your doctor will likely change your due date to match the ultrasound measurements. This is normal and usually results in a more accurate due date.
When will my baby actually be born?
While your due date is at 40 weeks, normal full-term pregnancy ranges from 37-42 weeks. About 50% of first-time mothers deliver by 40 weeks and 5 days, while mothers who've given birth before often deliver slightly earlier. Only 5% of babies are born on their exact due date. Most babies (90%) arrive between 37-42 weeks, with the highest likelihood between 39-41 weeks.
How do I calculate my due date with irregular periods?
If you have irregular periods, calculating your due date from LMP may be less accurate. The best approach is to: 1) Use your best estimate of your last period and note that it may be adjusted, 2) Pay attention to early pregnancy symptoms and when they started, 3) Get an early dating ultrasound between 8-13 weeks for the most accurate dating. Your doctor will rely more heavily on ultrasound measurements if your cycles are irregular.
What's the difference between gestational age and fetal age?
Gestational age is calculated from the first day of your last menstrual period and is what most pregnancy discussions reference. Fetal age (also called conceptional age) is calculated from conception and is about 2 weeks less than gestational age. When your doctor says you're "12 weeks pregnant," they mean 12 weeks gestational age. The actual fetal age would be about 10 weeks.
Can my due date predict if I'll have a boy or girl?
No, your due date cannot predict your baby's sex. Gender is determined at conception by whether the sperm carries an X or Y chromosome. Old wives' tales about conception timing and gender (like the Shettles method) are not scientifically proven. The only reliable ways to determine gender are through ultrasound (typically accurate after 18-20 weeks), NIPT blood testing (after 10 weeks), or amniocentesis.
Understanding Your Results
Your Due Date
This is your estimated delivery date, calculated at exactly 40 weeks from your LMP. Mark this date on your calendar, but remember that normal delivery can occur anytime between 37-42 weeks.
Current Week
Shows how many weeks pregnant you are right now. This helps you track your pregnancy progress, understand what's happening with your baby's development, and know which prenatal tests are coming up.
Trimester
Pregnancy is divided into three trimesters: First (weeks 1-12), Second (weeks 13-27), and Third (weeks 28-40). Each trimester brings different symptoms, baby developments, and medical checkups.
Days Remaining
A countdown to your due date. While exciting to track, remember this is an estimate. Focus on preparing for a two-week window around your due date rather than expecting delivery on an exact day.
Expert Tips for Expecting Parents
📅 Planning Around Your Due Date
- • Plan to stop working 1-2 weeks before your due date
- • Have your hospital bag packed by 36 weeks
- • Finish nursery preparations by 35 weeks
- • Schedule newborn care appointments in advance
- • Prepare for baby to arrive anytime after 37 weeks
⚠️ Important Reminders
- • First babies often arrive after the due date
- • Subsequent babies may come earlier
- • Due dates can change after ultrasounds
- • Every pregnancy is unique
- • Trust your healthcare provider's guidance