If you are unsure about cycle length, use 28 days.
This tool gives an estimate only and is not medical advice. Your healthcare provider may adjust your due date based on ultrasound and clinical assessment.
What is a due date calculator?
A due date calculator estimates your baby’s expected delivery date (EDD). Most pregnancies are measured at about 40 weeks from the first day of your last menstrual period, not from the day conception occurred. Because of that, many tools use your LMP as the starting point and then add 280 days.
This estimate is useful for planning prenatal appointments, understanding trimester timelines, and preparing for major milestones. Still, it is important to remember that due dates are a target, not a guarantee. Many healthy babies are born before or after the estimated date.
How this due date calculator works
Method 1: LMP (Last Menstrual Period)
If you know the first day of your last period, the calculator applies a standard obstetric formula:
- Base pregnancy length: 280 days from LMP
- Cycle-length adjustment: if your cycle is longer or shorter than 28 days, the estimate shifts accordingly
Example: if your cycle is 30 days, ovulation often occurs slightly later, so the estimated due date moves a little later as well.
Method 2: Conception date
If you know your conception date, the calculator adds 266 days (38 weeks). This method can be useful when ovulation timing is known, such as with ovulation tracking or fertility treatment.
What to expect from the results
After calculating, you will see:
- Your estimated due date
- Estimated gestational age today
- Days remaining until your due date (or days past due)
- Trimester status and key milestone dates
These details can help you stay organized and informed as your pregnancy progresses.
Why due dates can change
Even with good data, due dates are estimates. Providers may adjust dating if early ultrasound measurements suggest a different gestational age. Early ultrasounds are often more accurate for dating than period history alone, especially if cycles are irregular.
- Irregular cycles can make ovulation timing unpredictable
- Implantation timing varies from person to person
- Not all pregnancies reach exactly 40 weeks
Pregnancy timeline overview
First trimester (weeks 1–13)
This stage includes fertilization, implantation, and major early development. Common symptoms include fatigue, nausea, and breast tenderness.
Second trimester (weeks 14–27)
Many people feel more energy in this phase. Routine anatomy scans and growth checks usually happen during this period.
Third trimester (weeks 28–40+)
Growth accelerates and delivery preparation begins. Your provider may increase monitoring as you approach term.
Frequently asked questions
Is my due date the exact day I will give birth?
No. Only a small percentage of babies are born on their exact due date. A birth window around your due date is common and normal.
What if I do not remember my LMP?
Use the conception-date method if known, and discuss dating ultrasound options with your provider for better accuracy.
Should I rely only on an online calculator?
Use calculators for planning, but always follow your clinician’s guidance. Medical history, ultrasound findings, and prenatal exams matter more than a standalone tool.
Final note
A due date calculator is a practical way to estimate your timeline and stay prepared. Use it as a starting point, then confirm details with your obstetrician or midwife to get the most accurate pregnancy dating for your situation.