Baby Due Date Calculator
Calculate your estimated due date using multiple medically recognized formulas with trimester breakdown, cultural features, and prenatal screening dates
Enter the first day of your most recent menstrual period
Default is 28 days. Adjust if your cycle is regularly shorter or longer (20-45 days).
Used by the Mittendorf-Williams formula to adjust the due date
Enter a Date to Calculate
Select a calculation method and enter your date to see your estimated due date, trimester breakdown, formula comparison, and more.
How to Use the Baby Due Date Calculator
Choose Your Calculation Method
Select the method that matches your situation from the five available options: Last Menstrual Period (LMP), Conception Date, IVF Transfer Date, Ultrasound Dating, or Ovulation Date. If you are unsure, the LMP method is the most common and is used by most healthcare providers as the starting point for pregnancy dating. The LMP tab automatically appears when you open the calculator.
Enter Your Date and Adjust Settings
Enter the relevant date for your chosen method. For LMP, also enter your average cycle length if it differs from the standard 28 days — this adjusts all three formula results automatically. For the LMP and Mittendorf-Williams formula, select whether this is your first pregnancy or a subsequent one, as the Mittendorf-Williams formula uses different day counts for each. For IVF, select whether your embryo was a Day 3, Day 5, or Day 6 transfer. For ultrasound, enter the scan date and the gestational age in weeks and days shown on your report.
Review Your Due Date and Formula Comparison
Your estimated due date appears as the large hero result at the top of the results panel. Below it you will see your current gestational age, days remaining, and trimester status. Scroll down to see the Formula Comparison section, which shows your due date calculated using Naegele's Rule, Mittendorf-Williams, and Parikh's Formula side by side — giving you a range of estimates from three scientifically recognized methods. This is unique to this calculator and helps you understand the range of likely delivery dates.
Explore Charts, Cultural Features, and Screening Schedule
The pregnancy progress donut chart and trimester timeline bar give you visual snapshots of your pregnancy journey. In the cultural features section, see your baby's predicted Western zodiac sign, monthly birthstone, and Chinese zodiac animal based on the estimated due date. Click the screening schedule toggle to see a personalized table of key prenatal appointments and their estimated dates based on your EDD. Use the print button to save a copy of all your results.
Frequently Asked Questions
What is the difference between Naegele's Rule, Mittendorf-Williams, and Parikh's Formula?
Naegele's Rule is the oldest and most widely used formula, adding 280 days to the first day of your last menstrual period and adjusting for cycle length. The Mittendorf-Williams rule, published in 1990, found that first-time mothers tend to deliver at 288 days from LMP while mothers who have given birth before deliver at around 283 days. Some studies have found it to be roughly twice as accurate as Naegele's Rule. Parikh's Formula was specifically designed for women with irregular cycles: EDD equals LMP plus 9 months minus 21 days plus cycle length. For a 28-day cycle, Parikh's formula gives the same result as Naegele's, but for longer or shorter cycles it provides a different estimate. Seeing all three side by side helps you understand the realistic range of your delivery date.
How do I calculate my due date if I had IVF?
For IVF pregnancies, the calculation uses your embryo transfer date and the age of the embryo at the time of transfer. A Day 3 embryo transfer adds 263 days to the transfer date (because the embryo is already 3 days old out of the full 266-day fetal gestation from conception). A Day 5 blastocyst transfer adds 261 days, and a Day 6 blastocyst adds 260 days. This gives a very precise estimate because the exact timing of fertilization is known in IVF. Select the IVF Transfer Date method in this calculator, enter your transfer date, and choose the appropriate embryo age from the dropdown to get your result.
Why does my doctor sometimes give me a different due date than this calculator?
Healthcare providers may adjust your due date based on first-trimester ultrasound measurements, which are considered the most accurate method for pregnancy dating. If your crown-rump length (CRL) measurement at the ultrasound differs significantly from your LMP-based estimate — typically more than 5 to 7 days in the first trimester — your provider will often use the ultrasound date instead. The ultrasound reflects actual fetal development rather than an estimated fertilization date. It is also possible that your provider uses a slightly different cycle length assumption or a different formula. The due date shown by this calculator should be close to what your provider calculates, and the formula comparison feature shows the range of medically supported estimates.
Is it normal if I deliver before or after my due date?
Yes, absolutely. Only about 4 to 5 percent of babies are born on their exact due date. The estimated due date is a statistical midpoint based on population averages, not a precise prediction for any individual pregnancy. About 60 percent of full-term births occur within one week of the EDD, and about 90 percent occur within two weeks. A normal delivery window spans from 37 to 42 weeks of gestation. Babies born between 39 and 40 weeks and 6 days are considered full term. Between 37 and 38 weeks and 6 days is called early term, 41 weeks is late term, and 42 or more weeks is post-term. Your healthcare provider will monitor you closely in the final weeks and discuss options if your pregnancy goes significantly past your due date.
How accurate are online due date calculators compared to ultrasound dating?
LMP-based calculators like this one are a very good starting estimate, but they assume that your ovulation occurred on day 14 of a 28-day cycle, which is not true for everyone. Women with irregular cycles, polycystic ovary syndrome (PCOS), or cycles that vary significantly in length may find LMP-based results less accurate. First-trimester ultrasound is considered the most accurate dating method, with accuracy within 5 to 7 days. Second-trimester ultrasounds are accurate within about 7 to 14 days. This is why many providers will confirm or adjust the LMP-based estimate using an early ultrasound. Use this calculator as an excellent starting estimate and confirm with your healthcare provider.
What do the Chinese zodiac and Western zodiac results mean?
The zodiac and cultural results shown in this calculator are purely for fun and are based on your baby's estimated due date. The Western zodiac sign is determined by the calendar date of the EDD using the standard astrological date ranges. The monthly birthstone is the traditional gemstone associated with the birth month of the EDD. The Chinese zodiac animal is determined by the Chinese New Year of the year your baby is expected to be born — since Chinese New Year falls between late January and late February, babies born near that window may fall into the zodiac year before or after the standard calendar year. None of these cultural features have medical significance; they are intended as a fun addition to your due date calculation results.