Pregnancy
Due Date Calculator
Estimate your arrival date. Use our simple tool to find out when you’re likely to meet your new family member based on your last period.
How Is the Due Date Calculated?
The standard method for calculating a pregnancy due date is Naegele’s rule. This formula assumes a regular 28-day menstrual cycle and pregnancy lasting 280 days (40 weeks) from the first day of your last menstrual period (LMP).
Adjusting for Cycle Length
Not everyone has a standard 28-day cycle. If your cycle is longer or shorter, our calculator adjusts the estimated due date accordingly. For every day your cycle is longer than 28 days, we add a day to the due date. Conversely, for every day it’s shorter, we subtract a day. If you are still tracking fertile days, the Ovulation Calculator covers the earlier stage of planning.
Note: This tool is for estimation only. Please consult with your healthcare provider for medical confirmation.
Using the estimate well
Understanding Your Pregnancy Due Date Result
A due-date calculator estimates the expected date of delivery from the last menstrual period or another supplied date. Only a small proportion of births occur on the exact estimated date.
Online calculators simplify real life into a small number of inputs. Use this result as a transparent estimate that you can review, not as proof that a particular outcome will occur.
Enter consistent information
Enter the first day of the last menstrual period and usual cycle length when requested. Irregular cycles, uncertain dates, recent hormonal contraception and assisted reproduction need different dating information.
Before saving the answer, check the units, decimal points and assumptions shown by the tool. If you compare results later, use the same method so the trend is meaningful.
Interpret the number in context
Early pregnancy ultrasound can provide more reliable dating in many situations, and a clinician decides whether an estimated due date should be changed. The calculator does not confirm pregnancy or fetal wellbeing.
Contact a maternity professional for bleeding, severe pain, reduced fetal movement when movements are expected, signs of labour, or any urgent concern. Do not delay care because a calculator suggests a different date. For the months after delivery, the Breastfeeding Diet to Increase Milk Supply covers postpartum nutrition.
A practical next step
Use the estimate to begin planning appointments, then follow the date recorded by the maternity team after clinical assessment.
- Save the inputs with the date instead of recording only the final number.
- Look for a repeatable trend and avoid reacting to one unusually high or low result.
- Use qualified medical or coaching support when the decision affects health, treatment or safety.
Common questions
Is the result exact? No. It is the output of the displayed formula and the information entered. Measurement error and individual variation still apply.
How often should it be recalculated? Recalculate when the underlying inputs meaningfully change. Repeating it several times a day usually adds noise rather than useful information.
Can it replace professional advice? No. It is an educational planning aid and cannot assess symptoms, diagnose a condition or account for a complete personal history.