Pregnancy Due Date Calculator
What is a pregnancy due date?
A pregnancy due date is an estimate of when your baby is likely to be born. It is usually calculated from the first day of your last menstrual period (LMP) and assumes a typical 40-week pregnancy.
Only about a small percentage of babies are born exactly on their due date. Most arrive within a couple of weeks before or after.
How the calculator works
- Enter the first day of your last period (LMP).
- Enter your average cycle length in days (or use the default if unsure).
- Click Calculate to see your estimated due date and other details.
- Use Copy or Share to save your result for later.
The calculator uses Naegele’s rule (LMP + 280 days) and adjusts slightly if your cycle is shorter or longer than 28 days.
What you need to enter
- LMP date: The first day your last period started. This is the standard starting point in most due date calculations.
- Average cycle length: The number of days from the first day of one period to the first day of the next. Many people have a cycle around 28 days.
Tip: If you are not sure about your exact cycle length, you can keep it at 28 days. Your doctor or midwife can refine the estimate later using ultrasound.
What the result shows
- Estimated due date: The main date your pregnancy is expected to reach 40 weeks.
- Gestational age: An approximate number of weeks and days pregnant based on today’s date.
- Trimester: Whether you are in the first, second, or third trimester.
- Due window: A range of days around the due date where many babies arrive.
Pregnancy timeline by trimester
These ranges are general guidelines. Your healthcare provider may use slightly different week ranges.
Helpful tips
- Write down or save your due date so you can refer to it later.
- Use the calculator again if your doctor gives you a more accurate LMP or ultrasound date.
- Focus on a due “window” rather than one exact day to reduce stress.
Important limitations
- The calculator assumes a natural conception and a single baby.
- Ovulation can happen earlier or later than average, even with a regular cycle.
- Twins, IVF pregnancies, and some health conditions may use different dating methods.
Frequently asked questions
Why is my due date different from the one my doctor gave me?
Your doctor may use ultrasound measurements and medical history, which can provide a more accurate estimate than LMP alone. In that case, follow the date your healthcare provider gives you.
What if I do not remember my exact LMP?
You can enter the closest date you remember, but the result will be less precise. Make sure to tell your doctor that your LMP date is an estimate so they can adjust using ultrasound.
Can this calculator be used for IVF or fertility treatments?
IVF and some fertility treatments use specific embryo transfer or conception dates. Your clinic will provide a due date based on their protocol. This LMP-based tool is not ideal for those cases.
Does a longer or shorter cycle change my due date?
Yes. If you usually ovulate later (longer cycles) or earlier (shorter cycles), the calculator adjusts the estimate slightly to reflect that difference.
Important note
This tool is for general information only and does not replace medical care. Always confirm your dates with a qualified healthcare professional and follow their instructions for pregnancy monitoring and checkups.