Pregnancy Due Date Calculator (Estimated Due Date)
Use this pregnancy due date calculator to estimate your baby’s due date using the first day of your last menstrual period (LMP). This tool is based on a typical 28-day cycle and a 40-week pregnancy. Every pregnancy is unique – your healthcare provider is the best person to confirm your dates.
Calculate your estimated due date
Enter the first day of your last menstrual period and your usual cycle length. The calculator will estimate your due date and how far along the pregnancy might be today.
How is the due date calculated?
Most due date calculators use a method called Naegele’s rule. It estimates your due date by adding 280 days (40 weeks) to the first day of your last menstrual period if you have a regular 28-day cycle.
- LMP: first day of your last menstrual period
- Typical pregnancy length: about 40 weeks from LMP
- Cycle length adjustment: if your cycle is shorter or longer than 28 days, the estimate may be shifted by a few days
Only a small percentage of babies are born exactly on their due date. Most arrive within a window of about two weeks before or after.
If you had irregular cycles, fertility treatments (such as IVF) or you are unsure about your last period, an early pregnancy ultrasound can give a more accurate dating. Always discuss your individual situation with your healthcare provider.
Pregnancy Due Date Calculator – Frequently Asked Questions
How accurate is a due date calculator?
A due date calculator is only an estimate. Many factors can affect when labour starts, including cycle length, when ovulation occurred and how the pregnancy is developing. Ultrasound and your healthcare provider’s assessment usually provide a more accurate date.
Can I have a healthy baby if I deliver before or after my due date?
Yes. Many healthy babies are born a little before or after the estimated due date. Your healthcare team will monitor your pregnancy and talk with you if there are concerns about going too far past your due date or delivering very early.
Does this calculator work if my cycles are irregular?
If your cycle length changes from month to month, the estimate may be less accurate. In that case, an early ultrasound and your provider’s assessment are especially helpful for working out how far along you are.
What if I used IVF or fertility treatments?
People who conceive with IVF or other fertility treatments often have very precise dates for egg retrieval and embryo transfer. Your fertility clinic or obstetric provider will calculate a due date based on those dates, which is more accurate than an LMP calculator.
When should I contact a doctor or midwife?
You should contact a healthcare provider as soon as you think you are pregnant, or if you have any concerning symptoms such as heavy bleeding, severe pain, severe nausea and vomiting, or if something just does not feel right to you.