Pregnancy Due Date Calculator
Estimated due date from your last period, using Naegele's rule.
Overview
Estimates your due date and how far along you are, based on the first day of your last menstrual period. It gives an expected date to plan around, with the understanding that few babies arrive on the exact day.
How it works
The calculator uses Naegele's rule, the standard method for estimating a due date from the last menstrual period (LMP). It counts forward 280 days (40 weeks) from the first day of your LMP, which is the same as taking that date, subtracting three months, and adding seven days. This assumes a regular 28 day cycle, so an unusually long or short cycle can shift the estimate. An ultrasound, especially in the first trimester, can give a more precise date and may adjust this one.
How to use it
- Enter the first day of your last menstrual period.
- Read your estimated due date.
- See how many weeks along the estimate puts you.
- Treat the date as an estimate to plan around.
Examples
Naegele's rule
If your last period started on January 1, subtracting three months gives October 1, and adding seven days gives an estimated due date of October 8.
Planning window
Because timing varies, think in terms of a window around the date rather than a single guaranteed day.
FAQ
How accurate is the due date?
What if my cycle is not 28 days?
Can an ultrasound change my due date?
What does the week count mean?
Is my data uploaded?
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