Pregnancy Due Date Calculator
Choose your best way to calculate from 5 different methods.
About Pregnancy Due Date Calculator
Estimate Due Date & Pregnancy Timeline
Wondering "how many weeks pregnant am I?" or "when will my baby arrive?" At duedatecalculator.app, our Pregnancy Due Date Calculator can help you estimate your due date, getting you ready for this exciting journey. It's more than just a date; it's a detailed pregnancy timeline week by week, offering insights into every stage of your pregnancy. Our pregnancy calculator uses 5 recognized methods to provide you with a helpful estimation:
- First day of last menstrual period (LMP)
- Conception date
- IVF transfer date
- Ultrasound scan (gestational age)
- Reverse due date calculation
Knowing your due date and pregnncy timeline week by week is a great start; it offers you a general roadmap along your pregnancy journey. But remember, only about 5% of babies arrive on their exact due date, as a 2013 study of about 18,700 women in Australia found out. So consider this a guiding reference. The result is an estimate, not an exact date. The ACOG defines a full-term delivery as occurring between 39 0/7 weeks through 40 6/7 weeks, though the window for term pregnancy generally spans from 37 0/7 weeks through 41 6/7 weeks. So, don't be overly anxious if your baby isn't born on the exact due date. Also, our calculator can't replace a doctor's confirmation. During your first prenatal visit, your doctor will confirm or adjust the due date based on your menstrual history, ultrasound results, and other factors. Always take the doctor's confirmed due date as the standard.
| Method | Input Required | Calculation | Accuracy Notes |
|---|---|---|---|
| LMP | First day of last period | Due Date = LMP + 280 days
or
Due Date = LMP + 9 months + 7 days | May vary for irregular cycles |
| Conception Date | Date of conception | Due Date = Conception Date + 266 days | Requires precise ovulation data |
| IVF Transfer | Embryo transfer date (day-3 or day-5) | Due Date (Day-3 Transfer) = IVF Transfer Date + 263 days
Due Date (Day-5 Transfer) = IVF Transfer Date + 261 days | Determined by procedure date |
| Ultrasound | Fetal measurements (e.g., CRL) | Due Date = Ultrasound Date + (40 weeks - Gestational Age at Scan) | Considered the clinical standard for dating |
| Reverse Calculation | Known due date | Current Gestational Age = 40 weeks - (Due Date - Current Date) / 7 | Useful for timeline, not due date generation |
References
- Predicting date of birth and examining the best time to date a pregnancy
https://pubmed.ncbi.nlm.nih.gov/23932061- Definition of Term Pregnancy - ACOG
https://www.acog.org/clinical/clinical-guidance/committee-opinion/articles/2013/11/definition-of-term-pregnancy- Methods for Estimating the Due Date - ACOG
https://www.acog.org/clinical/clinical-guidance/committee-opinion/articles/2017/05/methods-for-estimating-the-due-date
This is the most common method for calculating a pregnancy due date. It's based on the first day of your last menstrual period (LMP). This calculation is based on the standard medical assumption of a regular 28-day menstrual cycle with ovulation occurring on day 14, a method widely used by institutions like the Cleveland Clinic. To estimate your due date, our pregnancy calculator typically adds 280 days (or 40 weeks) to the first day of your LMP. Alternatively, a formula known as Naegele's Rule, is a standard obstetric method used to estimate the Expected Date of Confinement (EDC).
Formula:
Due Date = LMP + 280 days
or
Due Date = LMP - 3 months + 1 year + 7 days
For example, if your LMP began on January 1, 2025, your estimated due date would be around October 8, 2025. This method is simple, but keep in mind it might be less precise for women with irregular cycles or ovulation timing that deviates from day 14. It's a fantastic starting point for your pregnancy week calculator journey and helps you calculate due date from LMP.
References
- Menstrual Cycle - Cleveland Clinic
https://my.clevelandclinic.org/health/articles/10132-menstrual-cycle- Calculating a Due Date - Johns Hopkins Medicine
https://www.hopkinsmedicine.org/health/wellness-and-prevention/calculating-a-due-date
If you know the exact conception date, our conception calculator can provide a personalized baby due date estimation. Standard obstetric guidelines estimate a due date as 280 days (40 weeks) from the Last Menstrual Period. Based on a standard 28-day cycle where conception occurs around day 14 , this method estimates the due date by adding 266 days (38 weeks) to your known conception date. This method is especially handy if you've been closely tracking ovulation using kits or fertility apps.
Formula:
Due Date = Conception Date + 266 days
For instance, if conception occurred on March 1, 2025, your estimated due date would be around December 7, 2025. This can create a more tailored pregnancy calendar based on conception date. Just remember, pinpointing the exact conception date can sometimes be tricky unless ovulation was closely monitored.
References
- Menstrual Cycle - Cleveland Clinic
https://my.clevelandclinic.org/health/articles/10132-menstrual-cycle
For pregnancies achieved through in vitro fertilization (IVF), our IVF due date calculator is specifically designed for you. The due date is calculated based on your embryo transfer date and its developmental stage. To align with the standard obstetric timeline of 266 days from conception, this calculation adjusts for the embryo's existing age at transfer. By subtracting the days the embryo has already developed, the formula adds 263 days for a Day-3 transfer (266 minus 3) and 261 days for a Day-5 transfer (266 minus 5). These numbers account for how developed the embryo was at transfer.
Formula:
Due Date (Day-3 Transfer) = IVF Transfer Date + 263 days
Due Date (Day-5 Transfer) = IVF Transfer Date + 261 days
For example, if you had a 5-day transfer on April 1, 2025, your due date would be around December 18, 2025. This method often offers a more direct calculation due to the controlled nature of IVF procedures, helping you calculate due date from IVF and map out your pregnancy calendar.
According to ACOG, a first-trimester ultrasound is considered the most accurate method for establishing or confirming gestational age. Sonographers measure the Crown-Rump Length (CRL)—the length of the embryo from the top of the head to the bottom of the torso—to determine age. The due date is calculated by adding the remaining weeks needed to reach 40 weeks of gestation.
Formula:
Due Date = Ultrasound Date + (40 weeks - Gestational Age at Scan)
For example, if an ultrasound at 8 weeks shows a CRL corresponding to 8 weeks gestational age, the due date is 32 weeks from the scan date. This method is particularly valuable when the LMP is unknown or cycles are irregular. Clinical guidelines suggest that dating scans are most precise when performed between 8 and 12 weeks of gestation. This timeframe marks when the quickest and most consistent growth rates occur, and gestational age can be estimated accurately to within about 5 days.
References
- Methods for Estimating the Due Date - ACOG
https://www.acog.org/clinical/clinical-guidance/committee-opinion/articles/2017/05/methods-for-estimating-the-due-date- Sonography Assessment of Gestational Age - NIH
https://www.ncbi.nlm.nih.gov/books/NBK570610
Perhaps you already have an estimated due date from your doctor or a previous calculation. Our reverse due date calculator is perfect if you want to understand your pregnancy timeline week by week or estimate your conception date. Just input your known due date, and our tool will work backward for you.
Formula:
Current Gestational Age = 40 weeks - (Days remaining until Due Date / 7)
For instance, if your due date is October 8, 2025, and today is June 23, 2025, our tool can show you you're about 24 weeks and 5 days pregnant. This feature of our pregnancy week calculator by due date helps you connect the dots of your early pregnancy journey and align with those trimester milestones.
Your Personalized Pregnancy Timeline, At a Glance!
After calculation, you'll receive a detailed result. Along with a current stage summary showing your estimated weeks and days pregnant, you'll get a complete pregnancy timeline week by week table. This interactive table clearly outlines each week's date range, trimester, and important milestones. Remember, only about 5% of babies arrive on their exact due date, so consider this a guiding reference for your exciting journey ahead.