Pregnancy Due Date Calculator: Estimate Your Baby's Arrival
Finding out your estimated due date is one of the most exciting milestones of pregnancy. Our Pregnancy Due Date Calculator estimates your due date based on the first day of your last menstrual period (LMP) or your conception date. While only 5% of babies arrive exactly on their due date, knowing the estimated window helps you prepare for your baby's arrival and track your pregnancy progress week by week. Use our Pregnancy Due Date Calculator to estimate your costs.
How Due Dates Are Calculated
The standard method uses Naegele's Rule: add 280 days (40 weeks) to the first day of your last menstrual period. This assumes a 28-day cycle with ovulation occurring on day 14. If you know your conception date or ovulation date, the calculator adds 266 days (38 weeks) from that date.
Due dates are estimates based on averages. Gestation is considered full-term at 39-40 weeks, early-term at 37-38 weeks, and late-term at 41 weeks. Babies born between 37 and 42 weeks are generally considered healthy.
Using the Due Date Calculator
Enter the first day of your last menstrual period and your average cycle length (if not 28 days). The calculator shows your estimated due date, current gestational age in weeks and days, and the trimester you are in. You can also enter a conception date if known for a more precise estimate.
The calculator also shows important milestones: when the heart starts beating (week 6), when organs develop (weeks 8-12), when movement is felt (weeks 16-22), and when the baby is considered viable (week 24).
Pregnancy Timeline
First Trimester (Weeks 1-12)
Major organ development occurs. Common symptoms include morning sickness, fatigue, and breast tenderness. Most miscarriages occur during this period. Prenatal vitamins with folic acid are essential during these weeks to prevent neural tube defects.
Second Trimester (Weeks 13-26)
Morning sickness typically subsides. The baby begins to move, and the belly becomes visibly pregnant. Anatomy scan (ultrasound) is performed around week 20 to check development and often reveal the baby's sex. Many women find this trimester the most comfortable.
Third Trimester (Weeks 27-40)
The baby gains weight rapidly and organs mature. Common symptoms include back pain, Braxton-Hicks contractions, and frequent urination. The baby usually settles into a head-down position around week 34-36. Preparation for labor and delivery intensifies during this period.
Factors Affecting Due Date Accuracy
- Cycle length: Women with longer or shorter cycles ovulate at different times. The calculator adjusts for your cycle length to improve accuracy.
- First-trimester ultrasound: The most accurate method for dating a pregnancy. Ultrasound measurement of the crown-rump length between weeks 8-13 can estimate due date within 5-7 days.
- Irregular cycles: Women with irregular periods may have less accurate LMP-based estimates. Ultrasound dating is strongly recommended in these cases.
- Multiple pregnancies: Twins and triplets often arrive earlier than singletons. The average gestational age for twins is 36 weeks and for triplets is 32 weeks.
Preparing for Your Due Date
Use your estimated due date to plan maternity leave, prepare the nursery, and schedule prenatal appointments. However, keep in mind that due dates are estimates — pack your hospital bag by week 36, and consider that your baby may arrive any time between weeks 37 and 42. Talk to your healthcare provider about signs of labor and when to go to the hospital.
Start Calculating
Use our Pregnancy Due Date Calculator below to estimate your baby's arrival date and track your pregnancy progress. Also check our Ovulation Calculator for family planning and our Age Calculator to calculate your baby's age after birth.
Worked Example: From LMP to Due Date
Follow one pregnancy through the calculator to see how both methods land on the same answer. Suppose your last menstrual period began on January 1, 2027. The calculator builds a Date from that day and adds exactly 280 days, which is the standard 40-week estimate. January has 31 days, so the countdown runs through the rest of January, all of February (28 days in 2027), March, April, May, June, July, and August, and lands on October 8, 2027.
Now switch to the conception method and enter January 15, 2027 — the assumed day of conception, 14 days after the LMP. The calculator subtracts 14 days to recover January 1, then adds the same 280 days, so the due date is unchanged at October 8, 2027. That is why the two methods agree: Naegele's rule treats day 14 as ovulation day and works forward from there.
- The "Estimated Conception Date" line in the results is simply your LMP plus 14 days, so expect it to fall about two weeks after the period start.
- Your current pregnancy week is today's date minus the LMP divided into 7-day chunks, capped at 42 weeks — once it passes 42, the countdown line reads "Due date has passed."
- Because the rule assumes a 28-day cycle, a woman whose cycles run closer to 35 days ovulates later and may find the ultrasound-based date differs; an early scan is the tiebreaker.
- Only about 5% of births happen on the estimated date, so treat the window of 37 to 42 weeks as the real planning range.
Related Calculators
Use our Pregnancy Due Date Calculator Guide together with related tools such as BAC Calculator, BMI Calculator 01235915067, BMR Calculator to plan more accurately. Each calculator runs instantly in your browser with step-by-step guidance.
Written by the CalcMaster Pro Editorial Team — financial, health, and DIY tools reviewed for accuracy. All calculators run on standard, widely accepted formulas. Always confirm final numbers with a qualified professional for decisions that require official figures.