You can predict how pregnant you are by calculating from the first day of your last menstrual period (LMP).
Calculating Pregnancy Length
The standard way to estimate how pregnant you are is to count the weeks since the first day of your last menstrual period (LMP).
- Using the Last Menstrual Period (LMP): The due date is estimated to be 40 weeks, or 280 days, from the first day of your LMP. So the number of weeks that have passed since then is how far along you are in your pregnancy.
How it works
- Identify the first day of your last period: Note the date when your last menstrual period started.
- Count the weeks: Calculate the number of weeks from that date to the current date.
- For example, if your last period started on January 1st and today is April 1st, you would be roughly 13 weeks pregnant. (January has 31 days, February has 28 (in a non-leap year), and March has 31. A total of 90 days is approximately 13 weeks.)
- Estimate the due date: Add 40 weeks (280 days) to the first day of your LMP for your estimated due date.
- Consider Variations: Pregnancy length can vary slightly. Using your LMP is the most common method used.
Example Calculation
| Start of Last Period (LMP) | Current Date | Approximate Gestational Age |
|---|---|---|
| January 1st | April 1st | 13 weeks |
| June 1st | December 1st | 26 weeks |
| August 1st | November 1st | 13 weeks |
Remember that these are estimates, and your healthcare provider can provide a more accurate calculation based on your individual situation and sometimes through ultrasound.
