Pregnancy calculator
Due Date Calculator
Find your baby’s estimated due date from your last menstrual period or conception date. The calculator also shows pregnancy weeks, trimester, an estimated ovulation date and a due-date-based zodiac sign.
Standard pregnancy dating formulas
Runs in your browser
Clear estimate guidance
Method
How this pregnancy due date calculator works
This pregnancy due date calculator is built for the most common questions people ask: When is my baby due?, how many weeks pregnant am I? and what if I know my conception date instead of my period date? The calculator answers those questions in a simple way and then explains the formulas underneath.
| Method | Formula | Best used when | What to remember |
|---|---|---|---|
| Last menstrual period | EDD = LMP + 280 days + (cycle length − 28 days) | You know the first day of your last period. | Useful for regular cycles and everyday due-date estimates. |
| Conception date | EDD = conception date + 266 days | You know when conception or fertilization happened. | Helpful after ovulation tracking or fertility treatment. |
| Estimated ovulation date | Ovulation ≈ LMP + (cycle length − 14 days) | You want a cycle-adjusted estimate of the fertile midpoint. | It is an estimate, not a confirmed ovulation test result. |
| IVF guide | Day-5 transfer + 261 days or Day-3 transfer + 263 days | You conceived through IVF and know the transfer date. | IVF dating is often more precise because embryo age is known. |
Formula 1
40 weeks from the first day of the last menstrual period
This is the classic way to estimate a pregnancy due date for a typical 28-day cycle.
Formula 2
38 weeks from conception
This is the usual estimate when the conception or fertilization date is known.
Formula 3
Adjust cycle length when it is not 28 days
Longer cycles usually shift ovulation later, while shorter cycles can shift it earlier.
Examples
Due date examples you can check by hand
Many visitors want to know how to calculate due date manually before using a calculator. These examples make the math easier to follow.
| Starting point | Cycle length | Example method | Estimated due date |
|---|---|---|---|
| January 10, 2026 LMP | 28 days | Add 280 days | October 17, 2026 |
| January 10, 2026 LMP | 31 days | Add 280 days + 3 days | October 20, 2026 |
| February 1, 2026 conception | Not needed | Add 266 days | October 25, 2026 |
| Day-5 embryo transfer on March 1, 2026 | Not needed | Add 261 days | November 17, 2026 |
Helpful reminder:
A due date is a planning estimate, not a promise. It gives you a useful timeline for appointments, screening windows, nursery planning and pregnancy milestones.
Timeline
Pregnancy timeline by week and trimester
Knowing the estimated due date also helps you understand where you are in the pregnancy timeline. This quick view keeps the page useful for people searching for terms like pregnancy week calculator, how many weeks pregnant and trimester calculator.
Dating, early growth, first prenatal visits and the first-trimester scan usually happen here.
This is often when energy improves, the anatomy scan is done and baby movement becomes easier to notice.
This is the stretch when growth accelerates, birth planning gets more real and full-term delivery gets closer.
| Pregnancy stage | Weeks | What many people look for | Why the due date helps |
|---|---|---|---|
| Early pregnancy | 4–8 weeks | Positive test, first symptoms, first appointment | The due date creates the first timeline for care and expectations. |
| Dating and scan window | 8–13 weeks | How far along am I, ultrasound dating, first trimester | Dating can be confirmed or refined with early ultrasound. |
| Mid-pregnancy | 14–27 weeks | When will I feel movement, anatomy scan, second trimester | The due date anchors week-by-week milestone checks. |
| Late pregnancy | 28–40+ weeks | Hospital bag, full-term window, labor planning | The due date helps you think in a realistic delivery range instead of a single day. |
Accuracy
Why due dates change and why that is normal
There are several reasons why one due date estimate can differ from another. Many people do not ovulate exactly on day 14. Some people have shorter cycles, longer cycles or irregular periods. Others are not fully sure about the first day of the last period. That is why a due date calculator is best used as a smart estimate.
- The first day of the last period may be remembered incorrectly.
- Ovulation can happen earlier or later than the average cycle midpoint.
- Conception may not happen on the same day as intercourse.
- Early ultrasound can sometimes revise dating when the size does not match the period-based estimate.
What usually gives the most confidence?
A calculator is great for planning, but early pregnancy ultrasound is usually the best way to confirm or adjust the estimate when dates are uncertain.
If your provider gives you a due date after an ultrasound, use that as your main pregnancy timeline.
Health tips
What to do after you calculate your due date
Save the date somewhere simple
Add the estimated due date to your phone calendar so future pregnancy weeks are easier to track.
Think in a range, not a single day
Many births happen before or after the estimated due date, so a delivery window is more realistic than a fixed birthday.
Book early prenatal care
The due date helps plan the first visit, ultrasound timing and pregnancy screening windows.
Use your provider’s dating once confirmed
If a clinician updates the date after ultrasound, use that date going forward for appointments and milestones.
Trust and clarity
Why this page is useful
Two popular input paths
Use either the first day of the last period or the conception date, depending on what you know.
More than one answer
The page shows due date, pregnancy weeks, trimester, ovulation estimate and a full-term window instead of only one date.
Built for real readers
The page explains the math, covers common questions and keeps the language easy to follow.
Privacy-friendly
Your dates stay in your browser while the calculator runs on the page.
FAQ
Frequently asked questions about estimated due date
How is a due date calculated from the last menstrual period?
The standard estimate counts 280 days, or 40 weeks, from the first day of the last menstrual period. If your average cycle is longer or shorter than 28 days, the estimate can be shifted by the difference in cycle length.
How is a due date calculated from conception date?
If you know the conception or fertilization date, you can estimate the due date by adding 266 days, or 38 weeks.
How accurate is a due date calculator?
A due date calculator gives an estimate, not a guarantee. Many babies arrive before or after the estimated date. Early ultrasound is often used to confirm or adjust dating.
Can my due date change after an ultrasound?
Yes. If an early ultrasound shows a meaningful difference from last-period dating, a healthcare professional may revise the estimated due date.
What if I have irregular periods?
Last-period dating can be less reliable when periods are irregular, when ovulation happens earlier or later than expected, or when the first day of the last period is uncertain. In those situations, early ultrasound is especially helpful.
How is IVF due date timing usually estimated?
A common approach is to use the embryo transfer date and embryo age. For example, a day-5 embryo transfer is often estimated as 261 days until due date, while a day-3 transfer is often estimated as 263 days.
References
Evidence and guideline references
This page is written for general education and planning. It does not replace personal medical advice, diagnosis or treatment. If you are pregnant, the due date confirmed by your healthcare professional should guide your care.
- American College of Obstetricians and Gynecologists (ACOG): Methods for Estimating the Due Date
- Mayo Clinic: Pregnancy due date calculator
- Cleveland Clinic: Due Date Calculator
- NHS: Due date calculator
Medical note: This due date calculator is for informational use. Contact a qualified healthcare professional for symptoms, emergencies, irregular bleeding, pain, or questions about dating, ultrasound results or fertility treatment.